Foliar δ13C Research Articles

The effects of short-term rainfall variability on leaf isotopic traits of desert plants in sand-binding ecosystems

Sand-binding vegetation is effective in stabilizing sand dunes and reducing soil erosion, thus helps minimize the detrimental effects of desertification. The aim of this study is to better understand the relationships between water and nutrient usage of sand-binding species, and the effects of succession and rainfall variability on plants’ water–nutrient interactions. We examined the effects of long-term succession (50 years), inter-annual rainfall variability (from 65% of the mean annual precipitation in 2004 to 42% in 2005) and seasonality on water–nutrient interactions of three major sand-binding species (Artemisia ordosica, Hedysarum scoparium and Caragana korshinskii) by measuring foliar δ13C, δ15N and [N]. Long-term succession in general did not significantly alter δ13C, δ15N and [N] of the three species. Short-term rainfall variability, however, significantly increased foliar δ13C levels of all three species by 1.0–1.8‰ during the severely dry year. No significant seasonal patterns were found in foliar δ13C and δ15N values of the three species, whereas foliar [N] varied by season. For the two leguminous shrubs, the correlations between δ13C and δ15N were positive in both sampling years, and the positive correlation between [N] and δ13C was only found in the severely dry year. The results indicate that these sand-binding plants have developed into a relatively stable stage and they are able to regulate their nitrogen and water use in responding to environmental conditions, which reinforces the effectiveness of plantation of native shrubs without irrigation in degraded areas. However, the results also indicate that short-term climate variability could have severe impact on the vegetation functions.

Genotypic variation in foliar nutrient concentrations, δ13C, and chlorophyll fluorescence in relation to tree growth of radiata pine clones in a serpentine soil

AbstractThis study investigated the genotypic variation in foliar nutrient concentrations, isotopic signature (δ13C), and chlorophyll fluorescence (Fv/Fm) and tree growth of 40 radiata pine clones grown on a New Zealand serpentine soil, and the relationships between growth and physiological traits of these clones from improved and unimproved groups. Genotypic variation in growth and physiological traits existed within (i.e., clonal) and between groups, with larger variation among clones. The clonal repeatabilities were greater for foliar nitrogen (N), calcium (Ca), magnesium (Mg), boron (B) concentrations, δ13C, and Ca : Mg ratio (0.35–0.64) than for growth traits (0.14–0.27) and other physiological traits (0.08–0.24). Significant phenotypic correlations were found between growth traits and foliar phosphorus (P), potassium (K), sulfur (S), iron (Fe), and K : Mg and Ca : Mg ratios and Fv/Fm (positive), and foliar Mg (negative). This study indicates that the trees on this serpentine soil generally suffered from multiple nutrient deficiencies and imbalances and the clonal variation in growth performance was more related to their capabilities of acclimation to nutrient than water stresses. Overall, the clones that absorbed more P, K, S, and Fe and less Mg from the soil grew better on this serpentine soil. For unimproved clones, the most limiting nutrients for tree growth were foliar K and Fe, while for improved clones it was foliar K.

Foliar carbon isotope discrimination and related traits along light gradients in two different functional-type tree species

To understand how different plant functional types respond to light intensities, foliar carbon isotope discrimination (Δ13C) and related traits, i.e., specific leaf area (SLA), mass- and area-based nitrogen concentrations (Nmass and Narea), leaf dry mass content (LDMC) of two evergreen coniferous and three deciduous broad-leaved species, were measured under four light intensities. Foliar Δ13C and SLA increased significantly from full- to low-light conditions for all species. These indicate that species studied could increase their light capture capacity under low-light conditions, leading to lower water-use efficiency (higher 13C discrimination). There were significant differences in the responses of foliar Nmass or Narea to light variations in the two functional types, indicating that different functional-type tree species may have different N-use strategies to adapt to the light variations. It was found that there were large functional-type-dependent differences with regard to the relationships between foliar Δ13C and other leaf traits. Our findings suggest that all tree species could change foliar morphology to increase their light-harvesting ability under low-light conditions at the expense of decreasing their water-use efficiency. However, large differences in N-use strategy may exist between deciduous and evergreen species, which may be vital for the survival of these two functional-type tree species in a shaded understory. More important, our findings reveal that changes in Δ13C are not directly related to foliar N if N investment does not proportionally increase the photosynthetic capacity; this should be considered when exploring the relationships of nitrogen concentrations with Δ13C.

Grazing-Exclusion Effects on Aboveground Biomass and Water-Use Efficiency of Alpine Grasslands on the Northern Tibetan Plateau

The influences of grazing exclusion on plant species composition and intrinsic water-use efficiency (Wi) of alpine grasslands on the Northern Tibet Plateau are not well understood. We conducted a multisite transect field survey across the three main alpine ecosystems (meadow, steppe, and desert steppe) with nine pairs of grazing-excluded and adjacent open grazed pastures. Short-term grazing exclusion (started in 2006) did not result in significant changes in nutrients or bulk density of the surface soils (0–15cm), but it slightly changed the aboveground biomass (AGB) and coverage at both community and species levels. Community foliar δ13C and Wi differed among alpine grassland types, with values for steppe being similar to those for meadow and with desert steppe values being higher than both of these. Foliar δ13C and inferred Wi differed among the dominant species and varied negatively with precipitation and positively with temperature in 2010. These results confirm that there is an environmentally selective effect on the replacement of dominant species. There was no evident difference in foliar δ13C or Wi between grazing-excluded and open grazed sites, but there was a slight increase of AGB and coverage in grazing-excluded sites compared to open grazed ones at the species and community levels. These results indicated that grazing exclusion may have no clear influence on the physiological processes related to foliar water usage at the species level, but may have a cumulative effect on the carbon–water balance at the community level. Slight changes in linear regressions of foliar δ13C and Wi plotted across climatic gradients indicated that grasslands under grazing management might be more sensitive to regional climatic changes.

Ecological Facilitation between Two Epiphytes through Drought Mitigation in a Subtropical Rainforest

Positive species interactions (facilitation) play an important role in shaping the structures and species diversity of ecological communities, particularly under stressful environmental conditions. Epiphytes in rainforests often grow in multiple-species clumps, suggesting interspecies facilitation. However, little is known about the patterns and mechanisms of epiphyte co-occurrence. We assessed the interactions of two widespread epiphyte species, Asplenium antiquum and Haplopteris zosterifolia, by examining their co-occurrence and size-class association in the field. To elucidate factors controlling their interactions, we conducted reciprocal-removal and greenhouse-drought experiments, and nutrient and isotope analyses. Forty-five percent of H. zosterifolia co-occurred with A. antiquum, whereas only 17% of A. antiquum co-occurred with H. zosterifolia. Removing the fronds plus substrate of A. antiquum reduced the relative frond length and specific leaf area of H. zosterifolia, but removing fronds only had little effect. Removing H. zosterifolia had no significant effects on the growth of A. antiquum. H. zosterifolia co-occurring and not co-occurring with A. antiquum had similar foliar nutrient concentrations and δ15N values, suggesting that A. antiquum does not affect the nutrient status of H. zosterifolia. Reduced growth of H. zosterifolia with the removal of A. antiquum substrate, together with higher foliar δ13C for H. zosterifolia growing alone than those co-occurring with A. antiquum, suggest that A. antiquum enhances water availability to H. zosterifolia. This enhancement probably resulted from water storage in the substrate of A. antiquum, which could hold water up to 6.2 times its dry weight, and from reduced evapotranspiration due to shading of A. antiquum fronds. Greater water loss occurred in the frond-clipped group than the unclipped group between days 3–13 of the drought treatment. Our results imply that drought mitigation by substrate-forming epiphytes is important for maintaining epiphyte diversity in tropic and subtropic regions with episodic water limitations, especially in the context of anthropogenic climate change.

The relationship between the emerald ash borer (Agrilus planipennis) and ash (Fraxinus spp.) tree decline: Using visual canopy condition assessments and leaf isotope measurements to assess pest damage

Ash trees (Fraxinus spp.) in North America are being severely impacted by the invasive emerald ash borer (Agrilus planipennis Fairmaire) which was inadvertently introduced to the US in the 1990s from Asia. The emerald ash borer (EAB) is a phloem boring beetle which relies exclusively on ash trees to complete its life cycle. Larvae feed in the cambial tissue forming serpentine galleries that may girdle the tree, causing mortality in as little as two years. Although larval feeding is thought to be the cause of rapid tree mortality, the relationship between tree-level water stress and EAB larval activity has never been quantified. Identifying symptoms of an emerald ash borer outbreak at an early stage can facilitate informed management decisions. Although a user-friendly system of ash canopy condition rating has been used extensively to study EAB impacts, the mechanistic relationship between canopy ratings and EAB larval activity has not been quantified.The objective of this research was to use the stable carbon isotopic composition of canopy leaf tissue (foliar δ13C, a proxy of tree level water stress) to quantify the mechanism by which EAB causes tree mortality and to relate this mechanism to the ash canopy condition rating system. We found that as the canopy condition was rated as less healthy, EAB density and gallery cover increased, and foliar δ13C became more enriched as well. The rating system was able to identify trees in early stages of EAB infestation with relatively low levels of EAB (<20% gallery cover or<40EAB/m2). We also found that foliar δ13C and EAB larval gallery cover exhibited a significant positive correlation. These results suggest that as EAB larval feeding occurs, the tree canopy exhibits thinning, and as feeding continues the tree experiences chronic water stress and canopy dieback occurs. This study highlights the usefulness of the ash canopy condition rating system as a proxy of emerald ash borer densities at the tree level.

Relationships between C3 plant foliar carbon isotope composition and element contents of grassland species at high altitudes on the Qinghai-Tibet Plateau, China.

Relationships of foliar carbon isotope composition (δ13C) with foliar C, N, P, K, Ca, Mg contents and their ratios of 219 C3 species leaf samples, obtained in August in 2004 to 2007 from 82 high altitude grassland sites on the Qinghai-Tibet Plateau China, were examined. This was done with reference to the proposition that foliar δ13C increases with altitude and separately for the life-form groups of graminoids, forbs and shrubs and for the genera Stipa and Kobresia. For all samples, foliar δ13C was negatively related to foliar K, P and ∑K+ Ca+ Mg, and positively correlated to foliar C, C/N and C/P. The significance of these correlations differed for the taxonomic and life-form groups. Lack of a relationship of foliar δ13C with foliar N was inconsistent with the majority of studies that have shown foliar δ13C to be positively related to foliar N due to a decrease of Ci/Ca (the ratio between intercellular and atmospheric concentration of CO2) and explained as a result of greater photosynthetic capacity at higher foliar N concentration. However this inconsistency relates to other high altitude studies that have found that photosynthetic capacity remains constant as foliar N increases. After accounting for the altitudinal relationship with foliar δ13C, of the elements only the K effect was significant and was most strongly expressed for Kobresia. It is concluded that factors critical to plant survival and growth at very high altitudes, such as low atmospheric pressure and low temperatures, may preclude expression of relationships between foliar δ13C and foliar elements that have been observed at lower altitudes.

Carbon and nitrogen isotopic survey of northern peruvian plants: baselines for paleodietary and paleoecological studies.

The development of isotopic baselines for comparison with paleodietary data is crucial, but often overlooked. We review the factors affecting the carbon (δ13C) and nitrogen (δ15N) isotopic compositions of plants, with a special focus on the carbon and nitrogen isotopic compositions of twelve different species of cultivated plants (n = 91) and 139 wild plant species collected in northern Peru. The cultivated plants were collected from nineteen local markets. The mean δ13C value for maize (grain) was −11.8±0.4 ‰ (n = 27). Leguminous cultigens (beans, Andean lupin) were characterized by significantly lower δ15N values and significantly higher %N than non-leguminous cultigens. Wild plants from thirteen sites were collected in the Moche River Valley area between sea level and ∼4,000 meters above sea level (masl). These sites were associated with mean annual precipitation ranging from 0 to 710 mm. Plants growing at low altitude sites receiving low amounts of precipitation were characterized by higher δ15N values than plants growing at higher altitudes and receiving higher amounts of precipitation, although this trend dissipated when altitude was >2,000 masl and MAP was >400 mm. For C3 plants, foliar δ13C was positively correlated with altitude and precipitation. This suggests that the influence of altitude may overshadow the influence of water availability on foliar δ13C values at this scale.

Foliar δ(13)C response patterns along a moisture gradient arising from genetic variation and phenotypic plasticity in grassland species of Inner Mongolia.

Plants depend upon both genetic differences and phenotypic plasticity to cope with environmental variation over different timescales. The spatial variation in foliar δ13C levels along a moisture gradient represents an overlay of genetic and plastic responses. We hypothesized that such a spatial variation would be more obvious than the variation arising purely from a plastic response to moisture change. Leymus chinensis and Stipa spp. were sampled from Inner Mongolia along a dry-wet transect, and some of these species were transplanted to an area with a moisture gradient. For Stipa spp., the slope of foliar δ13C and mean annual precipitation along the transect was significantly steeper than that of foliar δ13C and mean annual precipitation after the watering treatment. For L. chinensis, there was a general decreasing trend in foliar δ13C under the different (increasing) watering levels; however, its populations showed an irregular relationship between foliar δ13C and moisture origin. Therefore, support for our hypothesis was obtained from Stipa spp., but not from L. chinensis.

The influence of weed control on foliar δ15N, δ13C and tree growth in an 8 year-old exotic pine plantation of subtropical Australia

Background and aims The aim of weed control and fertilization in forest plantations was to increase tree growth by reducing competition for available nutrients and water. However, treatments that influence weed biomass can also have significant impacts on soil carbon (C) and nitrogen (N) cycling which can in turn lead to changes in the dynamics of stable C (δ13C) and N (δ15N) isotope compositions in soils and tree foliage.

Relationships between altitudinal gradient and plant carbon isotope composition of grassland communities on the Qinghai-Tibet Plateau, China

Foliar and root carbon isotope composition (δ13C) of grassland communities on the Qinghai-Tibet Plateau, China, was obtained by the biomass weighting method and direct measurement. We investigated the characteristics and altitudinal patterns of foliar and root δ13C and determined which environmental factors influenced foliar δ13C most. Foliar δ13C of alpine steppe was significantly higher than that of alpine meadow and temperate steppe. For alpine meadow, root δ13C was significantly higher than of foliar δ13C. Foliar δ13C increased with altitude at an average rate of 0.60‰ km−1 for the whole grassland ecosystem. This rate was lower than that at species level. However, there were no significant relationships between root δ13C and altitude. Atmospheric pressure was a more important factor than temperature and precipitation in its influence on the altitudinal pattern of foliar δ13C at the community level.

Edge Effects on Foliar Stable Isotope Values in a Madagascan Tropical Dry Forest

Edge effects represent an inevitable and important consequence of habitat loss and fragmentation. These effects include changes in microclimate, solar radiation, or temperature. Such abiotic effects can, in turn, impact biotic factors. They can have a substantial impact on species, communities, and ecosystems. Here we examine clinal variations in stable carbon and nitrogen isotope values for trees along an edge-interior gradient in the dry deciduous forest at Ankarafantsika National Park. We predicted that soil respiration and differences in solar irradiance would result in stratified δ13C values where leaves collected close to the forest floor would have lower δ13C values than those growing higher up in the canopy. We also anticipated that plants growing at the savannah-forest boundary would have higher δ13C and δ15N values than plants growing in the forest interior. As expected, we detected a small but significant canopy effect. Leaves growing below 2 m from the forest floor exhibit δ13C values that are, on average, 1.1‰ lower than those growing above this threshold. We did not, however, find any relationship between foliar δ13C and distance from the edge. Unpredictably, we detected a striking positive relationship between foliar δ15N values and increasing distance into the forest interior. Variability in physiology among species, anthropogenic influence, organic input, and rooting depth cannot adequately explain this trend. Instead, this unexpected relationship most likely reflects decreasing nutrient or water availability, or a shift in N-sources with increasing distance from the savannah. Unlike most forest communities, the trees at Ampijoroa are growing in nutrient-limited sands. In addition to being nutrient poor, these well-drained soils likely decrease the amount of soil water available to forest vegetation. Continued research on plant responses to edge effects will improve our understanding of the conservation biology of forest ecosystems in Madagascar.

White spruce foliar δ13C and δ15N indicate changed soil N availability by understory removal and N fertilization in a 13-year-old boreal plantation

Background and aims Canada bluejoint grass is a strong competitor for water and N against young white spruce trees in regenerating boreal forests in moist habitats. We investigated foliar δ13C and δ15N responses of white spruce to understory removal and N fertilization to infer treatment effects on soil water and N dynamics.

Effect of leaf-cutting ant nests on plant growth in an oligotrophic Amazon rain forest

Abstract:This study examined whether high nutrient concentrations associated with leaf-cutting ant nests influence plant growth and plant water relations in Amazon rain forests. Three nests of Atta cephalotes were selected along with 31 Amaioua guianensis and Protium sp. trees that were grouped into trees near and distant (&gt;10 m) from nests. A 15N leaf-labelling experiment confirmed that trees located near nests accessed nutrients from nests. Trees near nests exhibited higher relative growth rates (based on stem diameter increases) on average compared with trees further away; however this was significant for A. guianensis (near nest 0.224 y−1 and far from nest 0.036 y−1) but not so for Protium sp. (0.146 y−1 and 0.114 y−1 respectively). Water relations were similarly species-specific; for A. guianensis, near-nest individuals showed significantly higher sap flow rates (16 vs. 5 cm h−1), higher predawn/midday water potentials (−0.66 vs. −0.98 MPa) and lower foliar δ13C than trees further away indicating greater water uptake in proximity to the nests while the Protium sp. showed no significant difference except for carbon isotopes. This study thus shows that plant response to high nutrient concentrations in an oligotrophic ecosystem varies with species. Lower seedling abundance and species richness on nests as compared with further away suggests that while adult plants access subterranean nutrient pools, the nest surfaces themselves do not encourage plant establishment and growth.

Ecophysiological comparison of 50-year-old longleaf pine, slash pine and loblolly pine

Longleaf pine (Pinus palustris Mill.), a species that once dominated the southeastern USA, is considered to be more drought tolerant than the principle plantation species in the South, loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.), and so is predicted to better cope with increases in drought frequency associated with climate change. To determine if longleaf pine displays a more conservative water use strategy than the other two southern pine species, we examined diurnal patterns in leaf light-saturated photosynthesis, stomatal conductance, water use efficiency and leaf water potential (ΨL) over one growing season in a 50-year-old replicated field experiment. Short-term photosynthetic response to temperature was examined in August. No consistent differences among species in leaf gas exchange rates were observed, but ΨL was higher in longleaf pine compared to loblolly and slash pine across the growing season. Foliar δ13C measured at the end of the growing season was higher in longleaf pine than in loblolly pine but not slash pine. No temperature optimum of photosynthesis was observed in any species and photosynthesis did not respond to changing temperature. Based on leaf physiological traits, these results do not support the contention that longleaf pine has a more conservative leaf water use strategy than the other two pine species. The results do suggest that differences in hydraulic architecture or hydraulic efficiency may account for higher ΨL and perhaps greater drought tolerance in longleaf pine.

The effects of Arceuthobium sichuanense infection on needles and current‐year shoots of mature and young Qinghai spruce (Picea crassifolia) trees

SummaryArceuthobium sichuanense is a hemiparasitic angiosperm that infects Qinghai spruce (Picea crassifolia Kom.) in Qinghai province, China, and causes severe damage to spruce forests in Qinghai‐Tibet Plateau. In this study, the impact of A. sichuanense infection on mature and young trees of Qinghai spruce was evaluated by examining needle and current‐year shoot morphology, needle water and nitrogen‐use efficiency (NUE) and needle nitrogen concentration. The most apparent effect of A. sichuanense infection was a significant reduction in both needle size distal to infection and current‐year shoot length in the infected branches (p &lt; 0.001). Per cent reductions in needle and current‐year shoot length were similar between mature and young trees (58.9 vs. 56.3%; 59.7 vs. 62.9%). There was a high degree of correlation in foliar δ15N values between the dwarf mistletoe and its host trees (R2 = 0.9017, p &lt; 0.001), while the foliar δ13C values of A. sichuanense were similar to those of infected mature and young spruce trees. The dwarf mistletoe infection also resulted in a significant decrease in host needle N concentration and δ13C values (p &lt; 0.001). The per cent reduction in needle N concentration in young trees was nearly twice as much as that in mature trees (20.49 vs. 11.54%), while the per cent reduction in needle δ13C values was similar between young and mature trees (−0.98 vs.−1.1‰). The NUE in mature trees was not affected by A. sichuanense infection, but the NUE in young trees was increased by the infection.

Inter- and intraspecific variations in bud phenology, foliar morphology, seasonal stomatal conductance and carbon isotopic composition in Cedrus libani and C. atlantica

Afforestation and reforestation activities enjoy a prominent place on the policy agenda as potential tools to sequester carbon and for biomass production to mitigate climate change and restoring marginal lands. Two provenances (1 from Turkey and 1 from Lebanon) of the species Cedrus libani A. Rich. and two provenances (1 from Morocco and 1 from France) of the species Cedrus atlantica (Endl.) Carrier were studied to evaluate to what degree these trees were suitable for afforestation in arid regions of Italy. We measured, seasonal stomatal conductance (g s), foliar morphology, foliar carbon isotopic composition (δ13C), growth, and assessed bud phenology in a split plot trials. Bud phenology showed that the Turkish and Lebanon provenances of C. libani gave rise to earlier buds (earlier bud provenances) than the Moroccan and French provenances of C. atlantica (later bud provenances) with a mean difference of 23.2 days. Both provenances showed similar bud phenology and seasonal stomatal conductance (g s) especially in April–May (earlier bud provenances) and June (later bud provenances). The foliar δ13C was negatively correlated with g s in both the earlier bud provenances (i.e., an increase in g s was accompanied by decreasing foliar δ13C values) and the later bud provenances. The stomatal conductance values measured over a growth season showed significant correlations with daily means of both temperature and relative humidity. Hence g s in the earlier bud provenances was correlated with daily temperature in spring, whereas correlations with relative humidity were found in later bud provenances in both late spring and summer. We concluded that the earlier bud provenances (C. libani) are not suitable in areas affected by both summer drought and late spring frosts, whereas the later bud provenances (C. atlantica) are more suitable to be used in future afforestation plans due to their greater tolerance to summer drought.

红池坝草地常见物种叶片性状沿海拔梯度的响应特征

Leaf Mass per Area(LMA),mass-and area-based nitrogen content(leaf N per unit area,Narea;leaf N per unit mass,Nmass) and foliar δ13C are fundamental leaf traits,describe dry mass in leaves and the return on investments of nutrients,and operates largely independently of growth form,plant functional type or biome.As a reflection of the per-area cost of producing new leaves,LMA significantly correlates with leaf N.Leaf N is strongly correlated with photosynthetic capacity,as N is essential for the synthesis of Rubisco,the key enzyme of photosynthesis.Foliar δ13C is associated with the p(CO2)i/p(CO2)a(intercellular/ambient partial pressure) ratios of CO2 that are also highly correlated with photosynthesis.These correlations provide a useful link between processes on short-term leaf-level scales and on long-term plant-and community-level scales.Understanding the patterns of these fundamental traits is essential for predicting ecosystem functioning in response to environmental change.To date,the most representative research about leaf traits and foliar δ13C has been carried out by Krner et al and Wright et al at the global scale and their findings have been confirmed in other studies.Nevertheless,there remains the opportunity for further studies on the adaptive significance and function of leaf traits in different environments and for different species.And changes of leaf traits along an altitudinal gradient are of particular use in the study of the adaptive characters of plants under the influences of environmental changes.In this study,five common species of the grassland,Trifolium pratense,Geranium wilfordii,Aster tataricus,Leontopodium leontopodioides and Spiraea prunifolia,were particularly studied on the altitudinal transect(815—2545 m) in Hongchiba(109°58′ E,31°30′ N),Chongqing.To measure LMA,mature,fully expanded and healthy leaves were harvested from the middle of plants of each of the five species in plots along the altitudinal gradient(not all species occurred in all plots).We avoided aging,discolored,and damaged leaves.The leaves were placed on A4 paper(21 cm×29.7 cm) with a background of a black cloth sized 1 m2,and then photographed using a camera on a tripod.The leaves were then dried in an oven at 85 ℃ for 24 hours and weighed to 0.01 g.ENVI software was used to calculate the leaf area/A4 paper area ratio,and together with leaf weight to calculate LMA.Leaf samples were crushed by a mortar and then measured for N and 13C on a Finnigan MAT253 isotope ratio mass spectrometer to a precision of ±0.1‰.The patterns of leaf traits(including leaf mass per area(LMA),leaf nitrogen content,and foliar δ13C) were analyzed both for all data pooled(n=56) and specific species.The results showed that in all data pooled,LMA,Narea and foliar δ13C had positive correlations with altitude;the pattern of Nmass was not significantly;LMA and Narea showed significantly positive relationships with foliar δ13C;the adaptive features of leaf traits among different species were not consistent.Leaf traits of S.prunifolia and G.wilfordii showed the same trends as all data pooled along the altitudinal gradient,whereas,T.pretense,A.tataricus and L.leontopodioides showed different patterns with increasing altitude.

Adaptive characteristics of grassland community structure and leaf traits along an altitudinal gradient on a subtropical mountain in Chongqing, China

Community structure and leaf traits are important elements of terrestrial ecosystems. Changes of community structure and leaf traits are of particular use in the study of the influence of climate change on terrestrial ecosystems. Patterns of community structure (including species richness, above- and below-ground biomass) and leaf traits (including leaf mass per area (LMA), nitrogen content both on mass and area bases (N mass and N area), and foliar δ13C) from 19 grassland plots along an altitudinal transect at Hongchiba in Chongqing, China, were analyzed. Species richness along the altitudinal transect had a hump-shaped pattern. Above-ground biomass had a quadratic decrease along the altitudinal gradient whereas below-ground biomass had the opposite pattern. Change of above-ground biomass of various taxonomic groups with altitude was also studied. Poaceae showed strong negative relationships and Asteraceae showed a hump-shaped relationship with increase of altitude. Five common species of the grassland, Trifolium pratense, Geranium wilfordii, Aster tataricus, Leontopodium leontopodioides, and Spiraea prunifolia, were particularly studied for variation of leaf traits along the altitudinal gradient. Averaged for all species, LMA, N area and foliar δ13C had positive correlations with altitude. N mass did not change significantly as altitude increased. LMA and N area showed significant positive relationships with foliar δ13C. The adaptive features of leaf traits among different species were not consistent. The study highlights specific adaptation patterns in relation to altitude for different plant species, provides further insights into adaptive trends of community structure and leaf traits in a specific ecological region filling a gap in the definition of global patterns, and adds to the understanding of how adaptive patterns of plants may respond to global climate change.

Nutrients limit photosynthesis in seedlings of a lowland tropical forest tree species

We investigated how photosynthesis by understory seedlings of the lowland tropical tree species Alseis blackiana responded to 10 years of soil nutrient fertilization with N, P and K. We ask whether nutrients are limiting to light and CO(2) acquisition in a low light understory environment. We measured foliar nutrient concentrations of N, P and K, isotopic composition of carbon (δ(13)C) and nitrogen (δ(15)N), and light response curves of photosynthesis and chlorophyll fluorescence. Canopy openness was measured above each study seedling and included in statistical analyses to account for variation in light availability. Foliar N concentration increased by 20% with N addition. Foliar P concentration increased by 78% with P addition and decreased by 14% with N addition. Foliar K increased by 8% with K addition. Foliar δ(13)C showed no significant responses, and foliar δ(15)N decreased strongly with N addition, matching the low δ(15)N values of applied fertilizer. Canopy openness ranged from 0.01 to 6.71% with a mean of 1.76 ± 0.14 (± 1SE). Maximum photosynthetic CO(2) assimilation rate increased by 9% with N addition. Stomatal conductance increased with P addition and with P and K in combination. Chlorophyll fluorescence measurements revealed that quantum yield of photosystem II increased with K addition, maximum electron transport rate trended 9% greater with N addition (p = 0.07), and saturating photosynthetically active radiation increased with N addition. The results demonstrate that nutrient addition can enhance photosynthetic processes, even under low light availability.