Browsing by Subject "photosynthesis"

Now showing 1 - 18 of 18

Are shade tolerance, survival, and growth linked? Low light and nitrogen effects on hardwood seedlings
(1996) Walters, Michael B; Reich, Peter B
Variation in shade tolerance is a primary mechanism driving succession in northern deciduous forests. However, little is known about interspecific differences in the traits responsible for shade tolerance. Is shade tolerance due to the ability to grow or survive in deep shade, or both? How do plant morphology and photosynthesis relate to growth in shade? Is low light the sole critical stress determining differences in "shade tolerance" or do below ground resources interact with low light to affect growth and survival? In this study we address these questions for seedlings of Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. grown for 2 yr in outdoor shade houses in a complete factorial of low light (2 and 8% open sky) and nitrogen (forest soil and forest soil plus 200 kg N.ha-'.yr-'). For these seedlings we examined effects of light and nitrogen on the interrelationships among survival, growth, and shade tolerance and explored the physiological bases of shade tolerance by examining the relationship of plant morphology and photosynthesis to growth. Nitrogen amendments did not have a significant effect on any plant trait at either light level. In 8% light, growth and survival were highest for shade-intolerant Betula papyrifera and mid-tolerant Betula alleghaniensis, lower for shade-tolerant Ostrya and Acer, and lowest for disturbance-adapted Quercus. In 2% light, species rankings reversed as Ostrya and Acer had higher growth and survival than the other species. Second-year survival was strongly related to 1st-yr growth (P < 0.001), whereas relationships with 1st-yr plant mass and 1styr absolute growth rates were weak. Therefore, survival of shade-tolerant species at 2% light was related to their maintenance of positive growth, whereas intolerant species had growth near zero and high rates of mortality. In both 2 and 8% light photosynthetic rates on mass (but not area) bases and the proportion of the plant in leaves (leaf area ratio and leaf mass ratio) were positively related to growth. Greater rates of growth and survival for shade-tolerant species in very low light, and for intolerant species in higher light, suggest that there is a species-based trade-off between maximizing growth in high light and minimizing the light compensation point for growth. This trade-off may be an important mechanism driving forest community dynamics in northern hardwood forests.
The biogeography, ecophysiology, and functional potential of phototrophic Chloroflexi in alkaline hot springs: from marker genes to metagenomes
(2022-07) Bennett, Annastacia
Alkaline hot springs in Yellowstone National Park (YNP) provide a framework to study the relationship between photoautotrophs and temperature. Previous work has focused on understanding how Cyanobacteria (oxygenic phototrophs) vary with temperature, sulfide, and pH – but many questions remain regarding the ecophysiology of anoxygenic photosynthesis due to the taxonomic and metabolic diversity of these taxa. Phototrophs within the Cyanobacteria and Chloroflexi groups are frequently observed in alkaline hot springs. Decades of research has determined that temperature constrains Cyanobacteria in alkaline hot springs, but factors that constrain the distribution of phototrophic Chloroflexi remain unresolved. In Chapter 1, I review the key findings from Chloroflexi isolate and in situ studies in the two hot springs that have been the focus of decades of work in YNP. I highlight the metabolic and ecological diversity of characterized phototrophic Chloroflexi as it relates to nitrogen fixation, carbon cycling, and sulfur cycling. Additionally, I introduce how foundational studies have informed next generation sequencing efforts in this dissertation and in other works. In Chapter 2, I examined the distribution of genes involved in phototrophy, carbon fixation, and nitrogen fixation in eight alkaline (pH 7.3-9.4) hot spring sites near the upper temperature limit of photosynthesis (~71ºC) in YNP using metagenome sequencing. Based on genes encoding key reaction center proteins, geographic isolation plays a larger role than temperature in selecting for distinct phototrophic Chloroflexi while genes typically associated with autotrophy in anoxygenic phototrophs did not have distinct distributions with temperature. However, I recovered Calvin Cycle gene variants associated with Chloroflexi, an alternative carbon fixation pathway in anoxygenic photoautotrophs. Lastly, I recovered several abundant nifH (nitrogen fixation gene) sequences associated with Roseiflexus providing further evidence that genes involved in nitrogen fixation in Chloroflexi are more common than previously assumed. Together, these results add to the body of work focused on the distribution and functional potential of phototrophic bacteria in Yellowstone National Park hot springs and support the hypothesis that a combination of abiotic and biotic factors impact the distribution of phototrophic bacteria in hot springs. In Chapter 3, I employed a combination of 16S rRNA gene sequencing and inorganic carbon photoassimilation microcosms, to test the hypothesis that temperature would constrain the activity and composition of phototrophic Cyanobacteria and Chloroflexi. I expected diversity and rates of photoassimilation to decrease with increasing temperature. I report 16S rRNA amplicon sequencing along with carbon isotope signatures and photoassimilation from 45-72ºC in two alkaline hot springs. I found that Roseiflexus, Chloroflexus (Chloroflexi) and Leptococcus (Cyanobacteria) operational taxonomic units (OTUs) have distinct distributions with temperature. This distribution suggests that, like phototrophic Cyanobacteria, temperature selects for specific phototrophic Chloroflexi taxa. The richness of phototrophic Cyanobacteria decreased with increasing temperature along with a decrease in oxygenic photosynthesis, whereas Chloroflexi richness and rates of anoxygenic photosynthesis did not decrease with increasing temperature, even as temperatures approaches the upper limit of photosynthesis (~72 - 73ºC). Our carbon isotopic data suggest an increasing prevalence of 3-hydroxypropionate bicycle (3-HPB) with decreasing temperature coincident with photoautotrophic Chloroflexi. Together these results indicate temperature plays a role in defining the niche space of phototrophic Chloroflexi (as has been observed for Cyanobacteria), but other factors such as morphology, geochemistry, or metabolic diversity of Chloroflexi, in addition to temperature, could determine the niche space of this highly versatile group. Finally, in Chapter 4, I build on the work in Rabbit Creek from Chapter 3 by conducting a phylogenomic and pangenome analysis of 17 Chloroflexales metagenome assembled genomes (MAGs). I hypothesized that Chloroflexus and Roseiflexus would harbor unique core genomes and that temperature would select for certain accessory genes. I built a phylogenomic tree with 17 Rabbit Creek MAGs and 15 NCBI isolate genomes and found that the Rabbit Creek MAGs represent genera with characterized isolates as well as novel taxa. I examined the functional potential of Roseiflexus and Chloroflexus MAGs and found that Roseiflexus core genomes were depleted in both 3-HPB and sulfide oxidation functions while Chloroflexus core genomes contained sulfide:quinone oxidoreductases (SQRs) and several steps in the 3-HPB. Furthermore, I found both Roseiflexus and Chloroflexus core genomes contained genes for carbon assimilation and storage, suggesting this is an integral function for Chloroflexi in the Rabbit Creek ecosystem. Lastly, I recovered several MAGs that did not align with reference genomes but contained genes for type-II reaction centers and thiosulfate oxidation. Additionally, the unclassified MAGs were more like other Rabbit Creek MAGs. This work builds on the body of work in phototrophic Chloroflexi in alkaline hot springs and further constrains the role of Chloroflexi in carbon and sulfur cycling.
Convergent acclimation of leaf photosynthesis and respiration to prevailing ambient temperatures under current and warmer climates in Eucalyptus tereticornis
(2016) Aspinwall, Michael J; Drake, John E; Campany, Courtney; Vårhammar, Angelica; Ghannoum, Oula; Tissue, David T; Reich, Peter B; Tjoelker, Mark G
Understanding physiological acclimation of photosynthesis and respiration is important in elucidating the metabolic performance of trees in a changing climate. Does physiological acclimation to climate warming mirror acclimation to seasonal temperature changes? We grew Eucalyptus tereticornis trees in the field for 14 months inside 9-m tall whole-tree chambers tracking ambient air temperature (Tair) or ambient Tair + 3°C (i.e. ‘warmed’). We measured light- and CO2-saturated net photosynthesis (Amax) and night-time dark respiration (R) each month at 25°C to quantify acclimation. Tree growth was measured, and leaf nitrogen (N) and total nonstructural carbohydrate (TNC) concentrations were determined to investigate mechanisms of acclimation. Warming reduced Amax and R measured at 25°C compared to ambient-grown trees. Both traits also declined as mean daily Tair increased, and did so in a similar way across temperature treatments. Amax and R (at 25°C) both increased as TNC concentrations increased seasonally; these relationships appeared to arise from source–sink imbalances, suggesting potential substrate regulation of thermal acclimation. We found that photosynthesis and respiration each acclimated equivalently to experimental warming and seasonal temperature change of a similar magnitude, reflecting a common, nearly homeostatic constraint on leaf carbon exchange that will be important in governing tree responses to climate warming.
Does physiological acclimation to climate warming stabilize the ratio of canopy respiration to photosynthesis?
(Wiley, 2016) Drake, John E; Tjoelker, Mark G; Aspinwall, Michael J; Reich, Peter B; Barton, Craig V. M.; Medlyn, Belinda E; Duursma, Remko A
Given the contrasting short-term temperature dependences of gross primary production (GPP) and autotrophic respiration, the fraction of GPP respired by trees is predicted to increase with warming, providing a positive feedback to climate change. However, physiological acclimation may dampen or eliminate this response. We measured the fluxes of aboveground respiration (Ra), GPP and their ratio (Ra/GPP) in large, field-grown Eucalyptus tereticornis trees exposed to ambient or warmed air temperatures (+3°C). We report continuous measurements of whole-canopy CO2 exchange, direct temperature response curves of leaf and canopy respiration, leaf and branch wood respiration, and diurnal photosynthetic measurements. Warming reduced photosynthesis, whereas physiological acclimation prevented a coincident increase in Ra. Ambient and warmed trees had a common nonlinear relationship between the fraction of GPP that was respired above ground (Ra/GPP) and the mean daily temperature. Thus, warming significantly increased Ra/GPP by moving plants to higher positions on the shared Ra/GPP vs daily temperature relationship, but this effect was modest and only notable during hot conditions. Despite the physiological acclimation of autotrophic respiration to warming, increases in temperature and the frequency of heat waves may modestly increase tree Ra/GPP, contributing to a positive feedback between climate warming and atmospheric CO2 accumulation.
Ecophysiological investigations of understory eastern redcedar in central Missouri
(1983) Lassoie, James P; Dougherty, Phillip M; Reich, Peter B; Hinckley, Thomas M; Metcalf, Clifford M; Dina, Stephen J
Eastern redcedar (Juniperus virginiana) is a sun-adapted, drought-resistant pioneer species common to pastures, abandoned fields, fence rows, and calcareous rock outcrops throughout the eastern United States. However, it is also a frequent component of the understory in mature oakhickory forests in central Missouri, where light levels are typically < 10% of full sunlight during much of the growing season. This is below eastern redcedar's reported optimum for photosynthesis. The competitive survival of understory eastern redcedar under such environmental conditions was apparently due to it being an evergreen conifer in a deciduous forest. Hence, its foliage was able to maintain a positive carbon dioxide balance throughout much of the year, with maximum net photosynthetic rates occurring during periods when the overstory was leafless. The greatest daily average net photosynthetic rates (Ph,) occurred during overstory leaf emergence when temperatures were moderate and light levels to the understory trees were annually the highest. Furthermore, since leaf temperatures and tree water deficits were relatively low at this time, daily gas exchange rates were not greatly limited by midday stomatal closure. After the overstory foliage had fully developed, understory light levels averaged -S50-800o below levels observed in early spring. Thus, photosynthesis was severely light limited during the day, resulting in Ph, that were 15-45% of the springtime maxima. The greatest daily average transpiration rates (TR) occurred during the summer due to the high evaporative demand. Increasing leaf temperatures and tree water deficits became more important by late summer, causing stomatal closure during some afternoons, which reduced Ph,, and TR to :730 and 40%, respectively, of the early summer levels. During the autumn, winter, and early spring, understory light levels were normally above the saturation point for photosynthesis. The light saturation point for an understory study tree (expressed as flux of photosynthetically active photons) was ;800 Armol m--2 s1, less than half of that reported for open-grown eastern redcedar. This relatively lower light saturation point suggested an adjustment to shade conditions. During the autumn overstory defoliation period, light levels to understory trees progressively increased, and Ph, eventually reached 80W of the springtime maximum. In contrast, TR only reached ;25% of the summer maximum, owing to relatively low evaporative demands. During the late autumn and winter, low leaf and soil temperatures combined to limit gas exchange severely. The major controlling factors seemed to be cold air temperatures directly inhibiting Ph, and cold soil temperatures indirectly producing tree water deficits due to reduced water uptake at the soil-root interface. Such conditions promoted persistent stomatal closure, resulting in Ph, near zero. However, a temporary warming trend during the winter caused an increase in Ph,, to a level -301O of the springtime maximum. Higher net photosynthetic rates probably were not possible due to the effects of low soil and air temperatures on the stomatal mechanism and on the photosynthetic apparatus.
Fire Affects Ecophysiology and Community Dynamics of Central Wisconsin Oak Forest Regeneration
(1990) Reich, Peter B; Abrams, Marc D; Ellsworth, David S; Kruger, Eric L; Tabone, Tom J
In order to understand better the ecophysiological differences among competing species that might influence competitive interactions after, or in the absence of, fire, we examined the response to fire of four sympatric woody species found in intermediatesized gaps in a 30-yr-old mixed-oak forest in central Wisconsin. Selected blocks in the forest were burned in April 1987 by a low-intensity controlled surface fire. The fire had significant effects during the following growing season on community structure, foliar nutrient concentrations, and photosynthesis. Acer rubrum seedling density declined by 70% following the fire, while percent cover increased several-fold in Rubus allegheniensis. In general, leaf concentrations of N, P, and K were increased by the fire in all species, although the relative enhancement decreased as the growing season progressed. Daily maximum photosynthetic rates were 30-50% higher in burned than unburned sites for Prunus serotina, Quercus ellipsoidalis, and R. allegheniensis, but did not differ between treatments for A. rubrum. Mean sunlit photosynthetic rates and leaf conductances were stimulated by the burn for all species, with the greatest enhancement in photosynthesis measured in Q. ellipsoidalis. Leaf gas exchange in R. allegheniensis was most sensitive to declining leaf water potential and elevated vapor pressure gradient, with Q. ellipsoidalis the least sensitive. Fire had no discernable effect on water status of these plants during a year of relatively high rainfall. In comparison with other species, A. rubrum seedlings responded negatively after fire-both in terms of survival/reproduction (decline in the number of individuals) and relative leaf physiological performance. Fire enhanced the abundance of R. allegheniensis and the potential photosynthetic performance of R. allegheniensis, P. serotina, and particularly Q. ellipsoidalis. We conclude that post-fire stimulation of net photosynthesis and conductance was largely the result of enhanced leaf N concentrations in these species.
Generality of leaf traits relationships: a test across six biomes
(Ecological Society of America, 1999) Reich, Peter B; Ellsworth, David S; Walters, Michael B; Vose, James M; Gresham, Charles; Volin, John C; Bowman, William D
Convergence in interspecific leaf trait relationships across diverse taxonomic groups and biomes would have important evolutionary and ecological implications. Such convergence has been hypothesized to result from trade-offs that limit the combination of plant traits for any species. Here we address this issue by testing for biome differences in the slope and intercept of interspecific relationships among leaf traits: longevity, net photosynthetic capacity (Amax), leaf diffusive conductance (Gs), specific leaf area (SLA), and nitrogen (N) status, for more than 100 species in six distinct biomes of the Americas. The six biomes were: alpine tundra–subalpine forest ecotone, cold temperate forest–prairie ecotone, montane cool temperate forest, desert shrubland, subtropical forest, and tropical rain forest. Despite large differences in climate and evolutionary history, in all biomes mass-based leaf N (Nmass), SLA, Gs, and Amax were positively related to one another and decreased with increasing leaf life span. The relationships between pairs of leaf traits exhibited similar slopes among biomes, suggesting a predictable set of scaling relationships among key leaf morphological, chemical, and metabolic traits that are replicated globally among terrestrial ecosystems regardless of biome or vegetation type. However, the intercept (i.e., the overall elevation of regression lines) of relationships between pairs of leaf traits usually differed among biomes. With increasing aridity across sites, species had greater Amax for a given level of Gs and lower SLA for any given leaf life span. Using principal components analysis, most variation among species was explained by an axis related to mass-based leaf traits (Amax, N, and SLA) while a second axis reflected climate, Gs, and other area-based leaf traits.
Geographic range predicts photosynthetic and growth response to warming in co-occurring tree species
(Nature Publishing Group, 2015) Reich, Peter B; Sendall, Kerrie M; Rice, Karen; Rich, Roy L; Stefanski, Artur; Hobbie, Sarah E; Montgomery, Rebecca A
Populations near the warm edge of species ranges may be particularly sensitive to climate change, but lack of empirical data on responses to warming represents a key gap in understanding future range dynamics. Herein we document the impacts of experimental warming on the performance of 11 boreal and temperate forest species that co-occur at the ecotone between these biomes in North America. We measured in situ net photosynthetic carbon gain and growth of >4,100 juvenile trees from local seed sources exposed to a chamberless warming experiment that used infrared heat lamps and soil heating cables to elevate temperatures by +3.4 °C above- and belowground for three growing seasons across 48 plots at two sites. In these ecologically realistic field settings, species growing nearest their warm range limit exhibited reductions in net photosynthesis and growth, whereas species near their cold range limit responded positively to warming. Differences among species in their three-year growth responses to warming parallel their photosynthetic responses to warming, suggesting that leaf-level responses may scale to whole-plant performance. These responses are consistent with the hypothesis, from observational data and models, that warming will reduce the competitive ability of currently dominant southern boreal species compared with locally rarer co-occurring species that dominate warmer neighbouring regions. © 2015 Macmillan Publishers Limited. All rights reserved.
Global effects of soil and climate on leaf photosynthetic traits and rates
(Wiley, 2015) Maire, Vincent; Wright, Ian J; Prentice, I. Colin; Batjes, Niels H; Bhaskar, Radika; Bodegom, Peter M; Cornwell, Will K; Ellsworth, David; Niinemets, Ülo; Ordonez, Alejandro; Reich, Peter B; Santiago, Louis S
Aim The influence of soil properties on photosynthetic traits in higher plants is poorly quantified in comparison with that of climate. We address this situation by quantifying the unique and joint contributions to global leaf-trait variation from soils and climate. Location Terrestrial ecosystems world-wide. Methods Using a trait dataset comprising 1509 species from 288 sites, with climate and soil data derived from global datasets, we quantified the effects of 20 soil and 26 climate variables on light-saturated photosynthetic rate (Aarea), stomatal conductance (gs), leaf nitrogen and phosphorus (Narea and Parea) and specific leaf area (SLA) using mixed regression models and multivariate analyses. Results Soil variables were stronger predictors of leaf traits than climatic variables, except for SLA. On average, Narea, Parea and Aarea increased and SLA decreased with increasing soil pH and with increasing site aridity. gs declined and Parea increased with soil available P (Pavail). Narea was unrelated to total soil N. Joint effects of soil and climate dominated over their unique effects on Narea and Parea, while unique effects of soils dominated for Aarea and gs. Path analysis indicated that variation in Aarea reflected the combined independent influences of Narea and gs, the former promoted by high pH and aridity and the latter by low Pavail. Main conclusions Three environmental variables were key for explaining variation in leaf traits: soil pH and Pavail, and the climatic moisture index (the ratio of precipitation to potential evapotranspiration). Although the reliability of global soil datasets lags behind that of climate datasets, our results nonetheless provide compelling evidence that both can be jointly used in broad-scale analyses, and that effects uniquely attributable to soil properties are important determinants of leaf photosynthetic traits and rates. A significant future challenge is to better disentangle the covarying physiological, ecological and evolutionary mechanisms that underpin trait–environment relationships.
Leaf life-span in relation to leaf, plant, and stand characteristics among diverse ecosystems
(1992) Reich, Peter B; Walters, M B; Ellsworth, D S
Variation in leaf life-span has long been considered of ecological significance. Despite this, quantitative evaluation of the relationships between leaf life-span and other plant and ecosystem characteristics has been rare. In this paper we ask whether leaf lifespan is related to other leaf, plant, and stand traits of species from diverse ecosystems and biomes. We also examine the interaction between leaf, plant, and stand traits and their relation to productivity and ecological patterns. Among all species, both mass- (Amass) and area-based (Aarea) maximum net photosynthesis decreased with- increasing leaf life-span, but the relationship was stronger on a mass (P < .001, r2 = 0.70) than an area (P < .05, r2 = 0.24) basis. Similarly, mass-based leaf nitrogen (leafNmass) decreased (P < .001, r2 = 0.52) with leaf life-span, but area-based leaf N (leaf Narea) did not (P > .25, r2 = 0.01). Specific leaf area (SLA, leaf area/leaf dry mass) and leaf diffusive conductance also decreased with increasing leaf life-span. Decreasing Amass with increasing leaf life-span results from the impact of decreasing Nmass and SLA on Amass· Variation in leaf traits as a function of leaflife-span was similar for broad-leaved and needle-leaved subsets of the data. These leaf-scale data from several biomes were compared to a data set from a single biome, Amazonia. For several leaf traits (e.g., SLA, Nmass• and Amass) the quantitative relationship with leaf life-span was similar in the two independent data sets, suggesting that these are fundamental relations applicable to all species. Amass was a linear function of Nmass (P < .001, r2 = 0.74) with a regression similar to previous analyses, while Aarea was not significantly related to Narea· These results suggest that the photosynthesis-leafN relationship among species should be considered universal when expressed on a mass, but not on a leaf arna, basis. Relative growth rates (RGR) and leaf area ratio (LAR, the whole-plant ratio of leaf area to total dry mass) of seedlings decreased with increasing leaflife-span (P < .001, r2 = 0.61 and 0.89, respectively). LAR was positively related to both RGR and Amass (r2 = 0.68 and 0.84, respectively), and Amass and RGR were also positively related (r2 = 0.55). Absolute height growth rates of young trees decreased with increasing leaf life-span (P < .001, r2 = 0.72) and increased with Amass (P < .001, r2 = 0.78). It appears that a suite of traits including short leaf life-span and high leafNmas"' SLA, LAR, and Amass interactively contribute to high growth rates in open-grown individuals. These traits interact similarly at the stand level, but stands differ from individuals in one key trait. In closed-canopy forests, species with longer lived foliage (and low LAR as seedlings) have greater foliage mass per unit ground area (P < .001, r2 = 0.74) and a greater proportion of total mass in foliage. The above ground production efficiency (ANPP /foliar biomass) of forest stands decreased markedly with increasing leaf life-span or total foliage mass (P < .001, r2 = 0.78 and 0.72, respectively), probably as a result of decreasing Amass• Nmam and SLA, all of which were positively related with production efficiency and negatively related to total foliage mass. However, high foliage mass of species with extended leaf life-spans appears to compensate for low production per unit foliage, since above ground net primary production (ANPP, in megagrams per hectare per year) of forest stands was not related to leaf life-span. Extended leaf life-span also appears to compensate for lower potential production per unit leaf N per unit time, with the result that stand-level N use efficiency is weakly positively related to leaf life-span. We hypothesize that co-variation among species in leaflife-span, SLA, leafNmam Amass• and growth rate reflects a set of mutually supporting traits that interact to determine plant behavior and production, and provide a useful conceptual link between processes at short term leaf scales and longer term whole plant and stand-level scales. Although this paper has focused on leaf life-span, this trait is so closely interrelated with several others that this cohort of leaf traits should be viewed as causally interrelated. Generality in the relationships between leaf life-span and other plant traits across diverse communities and ecosystems suggests that they are universal in nature and thus can provide a quantitative link and/ or common currency for ecological comparisons among diverse systems.
Maximum carbon assimilation model for understory wood plants growing at Bagley Nature Area in Duluth, MN
(2020-05-26) O'Connell, Erin M; Savage, Jessica A; oconn877@d.umn.edu; O'Connell, Erin M; Savage research team
These data were collected and analyzed for a project comparing the leaf phenology, carbon gain, growth, and freezing susceptibility of invasive and native species. Maximum seasonal carbon assimilation was modeled for six plants per eight species growing in a 50-year-old mixed forest. The model is based on understory light availability on sunny days, carbon dioxide assimilation rates, and leaf area adjusted in the spring for expanding leaves and in the fall for senescing leaves.
A novel soil manganese mechanism drives plant species loss with increased nitrogen deposition in a temperate steppe
(Wiley, 2016) Tian, Qiuying; Liu, Nana; Bai, Wenming; Li, Linghao; Chen, Jiquan; Reich, Peter B; Yu, Qiang; Guo, Dali; Smith, Melinda D; Knapp, Alan K; Cheng, Weixin; Lu, Peng; Gao, Yan; Yang, An; Wang, Tianzuo; Li, Xin; Wang, Zhengwen; Ma, Yibing; Han, Xingguo; Zhang, Wen‐Hao
Loss of plant diversity with increased anthropogenic nitrogen (N) deposition in grasslands has occurred globally. In most cases, competitive exclusion driven by preemption of light or space is invoked as a key mechanism. Here, we provide evidence from a 9-yr N-addition experiment for an alternative mechanism: differential sensitivity of forbs and grasses to increased soil manganese (Mn) levels. In Inner Mongolia steppes, increasing the N supply shifted plant community composition from grass–forb codominance (primarily Stipa krylovii and Artemisia frigida, respectively) to exclusive dominance by grass, with associated declines in overall species richness. Reduced abundance of forbs was linked to soil acidification that increased mobilization of soil Mn, with a 10-fold greater accumulation of Mn in forbs than in grasses. The enhanced accumulation of Mn in forbs was correlated with reduced photosynthetic rates and growth, and is consistent with the loss of forb species. Differential accumulation of Mn between forbs and grasses can be linked to fundamental differences between dicots and monocots in the biochemical pathways regulating metal transport. These findings provide a mechanistic explanation for N-induced species loss in temperate grasslands by linking metal mobilization in soil to differential metal acquisition and impacts on key functional groups in these ecosystems.
Photosynthesis and leaf nitrogen in five Amazonian tree species during early secondary succession
(1996) Ellsworth, D S; Reich, Peter B
Field measurements of maximum net photosynthesis (Pmax), leaf nitrogen (N) content (leaf N per area and percent N), and specific leaf area (SLA) were made for Amazonian tree species within and across early successional sites of known ages after abandonment from slash-and-burn agriculture. We examined five species across a successional sere near San Carlos de Rio Negro, Venezuela, to test whether plasticity was associated with successional status and to determine whether changes in foliar properties during secondary succession can be attributed to shifts in species composition, in resource availability, or both. Average leaf N concentration was high (nearly 3%) for a pioneer species (Cecropiaficifolia) early in succession (1-3 yr after abandonment) but was always lower for the other early and mid- to-late succession species, especially later in succession (1-2% at 5-10 yr after abandonment). Net photosynthetic capacity (P /area and P I mass) varied as much as sixfold, being higher in pioneer species such as Cecropia and Vismia on recently abandoned sites and lower in late successional species such as Miconia and Licania on 10-yr abandoned agricultural sites. Total daily light availability also varied widely (14-fold) from its peak 1 yr after farm abandonment to low levels 9 yr into succession. During the first 5 yr of secondary succession, there were significant (P < 0.05) differences in Pmax and leaf N concentration among species in any given year. In most species, Pmax values declined with increasing time since abandonment within any given site. There were important differences in photosynthetic plasticity among species: Pmax tended to be much greater in earlier than later successional species soon after abandonment. Also, the difference in Pmax among species narrowed (or reversed) over time since abandonment, largely because of decreasing Pmax in pioneer species. The results suggest that changes in both species composition and in resource availability combine to produce the common pattern of decreasing leaf N concentration and photosynthetic rates during early rain forest succession after agriculture. Early successional species showed strong (r2 - 0.57, P = 0.0001) mass-based photosynthesis-N relationships but weak (r2 = 0.40 or lower, P = 0.000 1) area-based relationships both across the secondary successional sere after agriculture and across sites varying in types of disturbance. Both mass- and area-based photosynthesis-N relationships were poorer or not significant (P > 0.05) for mid- to late-successional species. Higher instantaneous Pmax/N and greater slopes of the photosynthesis-N relationships in early than late successional species suggest that pioneer species may show greater carbon assimilation capacity with elevated leaf N concentration on early successional sites than co-occurring species. The data suggest that early and late successional species may differ in the mode and degree of leaf-level physiological plasticity across succession.
Plant phenology, growth, freezing damage, and carbon gain data observed from 2017 to 2018 on wood plants growing at Bagley Nature Area in Duluth, MN
(2020-05-26) O'Connell, Erin M; Savage, Jessica A; oconn877@d.umn.edu; O'Connell, Erin M; Savage research team
These data were collected for a project comparing the leaf phenology, carbon gain, growth, and freezing susceptibility of four invasive and four native species. Leaf phenology and stem growth were observed for ten individuals per understory wood shrubs species. Freezing damage was experimentally assessed for each species and minimum temperatures in the species' native and exotic ranges were determined. Carbon gain was modeled for six individuals per species based on photosynthetic light response curves, leaf phenology, and understory light.
Predicting leaf functional traits from simple plant and climate attributers using the GLOPNET global data set
(2007) Reich, Peter B; Wright, Ian J; Lusk, Christopher H
Knowledge of leaf chemistry, physiology, and life span is essential for global vegetation modeling, but such data are scarce or lacking for some regions, especially in developing countries. Here we use data from 2021 species at 175 sites around the world from the GLOPNET compilation to show that key physiological traits that are difficult to measure (such as photosynthetic capacity) can be predicted from simple qualitative plant characteristics, climate information, easily measured (“soft”) leaf traits, or all of these in combination. The qualitative plant functional type (PFT) attributes examined are phylogeny (angiosperm or gymnosperm), growth form (grass, herb, shrub, or tree), and leaf phenology (deciduous vs. evergreen). These three PFT attributes explain between one-third and two-thirds of the variation in each of five quantitative leaf ecophysiological traits: specific leaf area (SLA), leaf life span, mass-based net photosynthetic capacity (Amass), nitrogen content (Nmass), and phosphorus content (Pmass). Alternatively, the combination of four simple, widely available climate metrics (mean annual temperature, mean annual precipitation, mean vapor pressure deficit, and solar irradiance) explain only 5–20% of the variation in those same five leaf traits. Adding the climate metrics to the qualitative PFTs as independent factors in the model increases explanatory power by 3–11% for the five traits. If a single easily measured leaf trait (SLA) is also included in the model along with qualitative plant traits and climate metrics, an additional 5–25% of the variation in the other four other leaf traits is explained, with the models accounting for 62%, 65%, 66%, and 73% of global variation in Nmass, Pmass, Amass, and leaf life span, respectively. Given the wide availability of the summary climate data and qualitative PFT data used in these analyses, they could be used to explain roughly half of global variation in the less accessible leaf traits (Amass, leaf life span, Nmass, Pmass); this can be augmented to two-thirds of all variation if climatic and PFT data are used in combination with the readily measured trait SLA. This shows encouraging possibilities of progress in developing general predictive equations for macro-ecology, global scaling, and global modeling.
Simulating ozone effects on forest productivity: Interactions among leaf-, canopy-, and stand-level processes
(1997) Ollinger, Scott V; Aber, John D; Reich, Peter B
Ozone pollution in the lower atmosphere is known to have adverse effects on forest vegetation, but the degree to which mature forests are impacted has been very difficult to assess directly. In this study, we combined leaf-level ozone response data from independent ozone fumigation studies with a forest ecosystem model in order simulate the effects of ambient ozone on mature hardwood forests. Reductions in leaf carbon gain were determined as a linear function of ozone flux to the leaf interior, calculated as the product of ozone concentration and leaf stomatal conductance. This relationship was applied to individual canopy layers within the model in order to allow interaction with stand- and canopy-level factors such as light attenuation, leaf morphology, soil water limitations, and vertical ozone gradients. The resulting model was applied to 64 locations across the northeastern United States using ambient ozone data from 1987 to 1992. Predicted declines in annual net primary production ranged from 3 to 16% with greatest reductions in southern portions of the region where ozone levels were highest, and on soils with high water-holding capacity where drought stress was absent. Reductions in predicted wood growth were slightly greater (3–22%) because wood is a lower carbon allocation priority in the model than leaf and root growth. Interannual variation in predicted ozone effects was small due to concurrent fluctuations in ozone and climate. Periods of high ozone often coincided with hot, dry weather conditions, causing reduced stomatal conductance and ozone uptake. Within-canopy ozone concentration gradients had little effect on predicted growth reductions because concentrations remained high through upper canopy layers where net carbon assimilation and ozone uptake were greatest. Sensitivity analyses indicate a trade-off between model sensitivity to available soil water and foliar nitrogen and demonstrate uncertainties regarding several assumptions used in the model. Uncertainties surrounding ozone effects on stomatal function and plant water use efficiency were found to have important implications on current predictions. Field measurements of ozone effects on mature forests will be needed before the accuracy of model predictions can be fully assessed.
Simulating ozone effects on forest productivity: Interactions among leaf-, canopy-, and stand-level processes
(1997) Ollinger, Scott V; Reich, Peter B
Ozone pollution in the lower atmosphere is known to have adverse effects on forest vegetation, but the degree to which mature forests are impacted has been very difficult to assess directly. In this study, we combined leaf-level ozone response data from independent ozone fumigation studies with a forest ecosystem model in order simulate the effects of ambient ozone on mature hardwood forests. Reductions in leaf carbon gain were determined as a linear function of ozone flux to the leaf interior, calculated as the product of ozone concentration and leaf stomatal conductance. This relationship was applied to individual canopy layers within the model in order to allow interaction with stand- and canopy-level factors such as light attenuation, leaf morphology, soil water limitations, and vertical ozone gradients. The resulting model was applied to 64 locations across the northeastern United States using ambient ozone data from 1987 to 1992. Predicted declines in annual net primary production ranged from 3 to 16% with greatest reductions in southern portions of the region where ozone levels were highest, and on soils with high water-holding capacity where drought stress was absent. Reductions in predicted wood growth were slightly greater (3–22%) because wood is a lower carbon allocation priority in the model than leaf and root growth. Interannual variation in predicted ozone effects was small due to concurrent fluctuations in ozone and climate. Periods of high ozone often coincided with hot, dry weather conditions, causing reduced stomatal conductance and ozone uptake. Within-canopy ozone concentration gradients had little effect on predicted growth reductions because concentrations remained high through upper canopy layers where net carbon assimilation and ozone uptake were greatest. Sensitivity analyses indicate a trade-off between model sensitivity to available soil water and foliar nitrogen and demonstrate uncertainties regarding several assumptions used in the model. Uncertainties surrounding ozone effects on stomatal function and plant water use efficiency were found to have important implications on current predictions. Field measurements of ozone effects on mature forests will be needed before the accuracy of model predictions can be fully assessed.
Strong thermal acclimation of photosynthesis in tropical and temperate wet-forest tree species: The importance of altered Rubisco content
(Wiley, 2017) Scafaro, Andrew P; Xiang, Shuang; Long, Benedict M; Bahar, Nur H A; Weerasinghe, Lasantha K; Creek, Danielle; Evans, John R; Reich, Peter B; Atkin, Owen K
Understanding of the extent of acclimation of light-saturated net photosynthesis (An) to temperature (T), and associated underlying mechanisms, remains limited. This is a key knowledge gap given the importance of thermal acclimation for plant functioning, both under current and future higher temperatures, limiting the accuracy and realism of Earth system model (ESM) predictions. Given this, we analysed and modelled T-dependent changes in photosynthetic capacity in 10 wet-forest tree species: six from temperate forests and four from tropical forests. Temperate and tropical species were each acclimated to three daytime growth temperatures (Tgrowth): temperate – 15, 20 and 25 °C; tropical – 25, 30 and 35 °C. CO2 response curves of An were used to model maximal rates of RuBP (ribulose-1,5-bisphosphate) carboxylation (Vcmax) and electron transport (Jmax) at each treatment's respective Tgrowth and at a common measurement T (25 °C). SDS-PAGE gels were used to determine abundance of the CO2-fixing enzyme, Rubisco. Leaf chlorophyll, nitrogen (N) and mass per unit leaf area (LMA) were also determined. For all species and Tgrowth, An at current atmospheric CO2 partial pressure was Rubisco-limited. Across all species, LMA decreased with increasing Tgrowth. Similarly, area-based rates of Vcmax at a measurement T of 25 °C (Vcmax25) linearly declined with increasing Tgrowth, linked to a concomitant decline in total leaf protein per unit leaf area and Rubisco as a percentage of leaf N. The decline in Rubisco constrained Vcmax and An for leaves developed at higher Tgrowth and resulted in poor predictions of photosynthesis by currently widely used models that do not account for Tgrowth-mediated changes in Rubisco abundance that underpin the thermal acclimation response of photosynthesis in wet-forest tree species. A new model is proposed that accounts for the effect of Tgrowth-mediated declines in Vcmax25 on An, complementing current photosynthetic thermal acclimation models that do not account for T sensitivity of Vcmax25.

University Digital Conservancy

Browse by Subject

Browsing by Subject "photosynthesis"