The relative contributions of intra- and inter-specific variation in driving community stoichiometric responses to nitrogen deposition and mowing in a grassland

Leaf carbon, nitrogen, and phosphorus ecological stoichiometry of grassland ecosystems along 2,600-m altitude gradients at the Northern slope of the Tianshan Mountains

Ecological stoichiometry of terrestrial ecosystems has been a hot issue in current research, with intense focus on the proportional relationships of nutritional elements within plants and between plants and their environment. To clarify these relationships along continuous environmental gradients is essential for a more comprehensive understanding how plants adapt to a changing environment. In arid regions, the varying plant and soil types along altitude gradients offer a unique opportunity to examine the vertical spectrum of plant and soil ecological stoichiometry. In this study, the northern slope of the Tianshan Mountains was selected as the study area to explore the carbon (C), nitrogen (N), and phosphorus (P) ecological stoichiometric characteristics of herbaceous plants along 900-m-3,500-m altitude gradients. We also investigated the variation of ecological stoichiometric characteristics among different grassland types. The results indicated that the mean C, N, and P in leaf of grassland were 342.95 g·kg-1-557.73 g·kg-1, 6.02 g·kg-1-20.97 g·kg-1, and 0.71 g·kg-1-3.14 g·kg-1, respectively. There was no significant change in leaf carbon content along the elevation gradient, and the highest and lowest leaf C concentrations were in the upland meadow and the semidesert grasslands. Both N and P concentrations obtained their highest value in the meadow steppe. The P concentration gradually increased in desert and semidesert grasslands and reached the highest value in the meadow steppe, and then decreased to the lowest value in the upland meadow and subsequently increased in the alpine meadow. The ranges of the C:N ratio, C:P ratio, and N:P ratio were 16.36-155.53, 109.36-786.52, and 2.58-17.34, respectively. Due to fluctuations in the P concentration, the C:P ratio and N:P ratio reached the lowest value in the meadow steppe and obtained their highest value in the upland meadow. Redundancy analysis showed that temperature was the dominant factor affecting the C, N, and P ecological stoichiometry of herbaceous plants, followed by soil organic carbon, mean annual precipitation, soil pH, and soil electrical conductivity. Corresponding results could enhance predictive models of nutrient cycling and ecosystem responses to climate change, particularly in arid and semiarid regions.

Contrasting effects of plant inter- and intraspecific variation on community trait responses to nitrogen addition and drought in typical and meadow steppes

BACKGROUND

Inter- and intraspecific variation in plant traits play an important role in grassland community assembly under global change scenarios. However, explorations of how these variations contribute to the responses of community traits to nitrogen (N) addition and drought in different grassland types are lacking. We measured the plant height, leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf N content (LNC) and the ratio of leaf carbon (C) to leaf N (C:N) in a typical and a meadow steppe after three years of N addition, drought and their interaction. We determined the community-weighted means (CWMs) of the six traits to quantify the relative contribution of inter- and intraspecific variation to the responses of community traits to N addition and drought in the two steppes.

RESULTS

The communities in the two steppes responded to N addition and the interaction by increasing the CWM of LNC and decreasing C:N. The community in the meadow steppe responded to drought through increased CWM of LNC and reduced C:N. Significant differences were observed in SLA, LDMC, LNC and C:N between the two steppes under different treatments. The SLA and LNC of the community in the meadow steppe were greater than those of the typical steppe, and the LDMC and C:N exhibited the opposite results. Moreover, variation in community traits in the typical steppe in response to N addition and drought was caused by intraspecific variation. In contrast, the shifts in community traits in the meadow steppe in response to N addition and drought were influenced by both inter- and intraspecific variation.

CONCLUSIONS

The results demonstrate that intraspecific variation contributed more to community functional shifts in the typical steppe than in the meadow steppe. Intraspecific variation should be considered to understand better and predict the response of typical steppe communities to global changes. The minor effects of interspecific variation on meadow steppe communities in response to environmental changes also should not be neglected.

Responses of Ecological Stoichiometric Characteristics of Carbon, Nitrogen, and Phosphorus to Periodic Submergence in Mega-Reservoir: Growth of Taxodium distichum and Taxodium ascendens

Ecological stoichiometric studies can be useful for managing the deteriorated riparian zones of mega-reservoirs in which nutrients significantly impact the balanced vegetation cover. The present study aims to explore the effects of periodic submergence on the stoichiometric ecological characteristics of carbon (C), nitrogen (N), and phosphorus (P), as well as the growth conditions of two leading conifer species (Taxodium distichum and Taxodium ascendens) in the hydro-fluctuation zone of the Three Gorges Reservoir (TGR) region, China. The stoichiometrical contents of C, N, and P in fine roots, leaves, and branches, and the growth conditions of T. distichum and T. ascendens were measured in July 2019. The results showed that periodic submergence affected the stoichiometric characteristics and growth conditions of these two woody species, and the impact was restrained, but both grew well. The effects of inundation on the C, N, and P ecological stoichiometric characteristics differed in different parts of trees. In general, the C contents showed the following pattern: leaves > branches > fine roots. The N and P content showed the following pattern: leaves > fine roots > branches, while the C/N and C/P ratios showed an opposite trend to that of N and P. The N and P content in all parts of T. distichum (with means of 17.18 and 1.70 g/kg for leaves, 4.80 and 0.57 g/kg for branches, and 6.88 and 1.10 g/kg for fine roots, respectively) and T. ascendens (with means of 14.56 and 1.87 g/kg for leaves, 5.03 and 0.63 g/kg for branches, and 8.17 and 1.66 g/kg for fine roots, respectively) were higher than the national average level (with means of 14.14 and 1.11 g/kg for leaves, 3.04 and 0.31 g/kg for branches, and 4.85 and 0.47 g/kg for fine roots, respectively). Except for N and P contents in the leaves of T. distichum, there was a significant correlation between N and P elements in other parts (p < 0.05). Nevertheless, the N/P ratio (10.15, 8.52, 6.44, and 7.93, 8.12, 5.20 in leaves, branches, and fine roots of T. distichum and T. ascendens, respectively) was lower than the critical ratio of 14. The growth conditions of T. distichum and T. ascendens were significantly negatively correlated with their leaf C contents and significantly positively correlated with their fine root N and P contents. This study showed that T. distichum and T. ascendens could maintain their normal growth needs by properly allocating nutrients between different organs to adapt to the long periodic submergence in the hydro-fluctuation zone of the TGR region.

The relative contribution of intraspecific variation and species turnover to the community-level foliar stoichiometric characteristics in different soil moisture and salinity habitats

BACKGROUND

Trait-based approaches have been used to demonstrate the responses of plant functional traits to environmental change may manifest both among- and/or within-species. However, how community-level foliar stoichiometric characteristic variations respond to aridity and salinity is still not well-known.

METHODS

We calculated community weighted means (CWMs) and non-weighted means (CMs) of foliar C, N, and P concentrations (and their ratios) in a dryland plant community respond to high (HSW) and low soil moisture and salinity (LSW). Based on a sum of squares decomposition method, we determined the relative contributions of intraspecific variation and species turnover in both HSW and LSW habitats.

RESULTS

The CWMs of foliar C, C:N and C:P, and CM of N in the HSW habitat were significantly greater than those in the LSW habitat. The trait variations in two habitats were mainly driven by intraspecific variation, and its contribution to trait variation mostly declined with the decrease of soil moisture and salinity. The CWMs of foliar C-related stoichiometric characteristics were mainly dominated by species turnover in both habitats. Moreover, the contribution of species turnover to C and C:P variations showed an increasing trend in the LSW habitat. For CWMs, negative covariations between intraspecific variation and turnover occurred in HSW and positive covariations (except N:P) occurred in LSW; however, CMs were generally positively correlated in both habitats.

CONCLUSIONS

The intraspecific variation declined as drought stress intensified, which indicates that the adaptability of desert plants declined when the stress changed from salinity to aridity. The total variation of C-related traits in both habitats were mainly dominated by species turnover. These findings highlight the importance of intraspecific variation in driving desert plant response of community functional composition to salt stress, and the joint role of intraspecific variation and species turnover in resisting drought stress.

N:P stoichiometric changes via species turnover in arid versus saline desert environments

Aridity and salinity have a key role in driving physiological and ecological processes in desert ecosystems. However, how community-scale foliar nutrients respond to aridity and salinity, and how these responses might vary with community composition along aridity and salinity gradients is unclear. We hypothesize that the response will be a shift in community stoichiometric values resulting from nutrient variability of shared species and unique species (site-specific species), but little research has addressed the relative contribution of either component.We analyzed the community-scale stoichiometric response of a desert community of perennial plants along an aridity and salinity transect by focusing on foliar nitrogen (N) and phosphorous (P) concentrations and N:P ratios. After evaluating the shared and unique species variability, we determined their relative contribution to the community stoichiometric response to aridity and salinity, reflected by changes in nonweighted and weighted community-average values.Community-scale stoichiometry decreased significantly under aridity and salinity, with significantly consistent changes in nonweighted and weighted community-average stoichiometry for most shared and unique species measurements. The relative contribution of unique species shifts to the changes in community stoichiometry was greater (15%-77%) than the relative contribution of shared species shifts (7%-45%), excluding the change in weighted P concentration under aridity. Thus, the shifts of unique species amplified the community stoichiometric response to environmental changes. Synthesis. These results highlighted the need for a more in-depth consideration of shared and unique species variability to understand and predict the effects of environmental change on the stoichiometry of plant communities. Although variation in community stoichiometry can be expected under extreme aridity and salinity conditions, changes of unique species could be a more important driver of the stoichiometric response of plant communities.

Effects of Stellera chamaejasme removal on the nutrient stoichiometry of S. chamaejasme-dominated grasslands in the Qinghai-Tibetan plateau

BACKGROUND

Stoichiometric relations drive powerful constraints in several fundamental ecosystem processes. However, limited studies have been conducted on the ecological stoichiometry of plants after the change of community composition induced by Stellera chamaejasme removal in alpine grassland in the Qinghai-Tibetan Plateau.

METHODS

We investigated the effects of S. chamaejasme removal on ecological stoichiometry by estimating the C:N:P stoichiometry in species, functional group and community levels of the ecosystem. The interactions between different species, functional groups and correlation with soil nutrient, responding to S. chamaejasme removal were also analyzed.

RESULTS

For the plants that became dominant after S. chamaejasme removal (SR), N content decreased and their C:N increased. S. chamaejasme removal significantly affected the nutrient stoichiometry of different functional groups. Specifically, Gramineae in the SR sites had decreased N content and N:P, and increased C:N; however, forbs had increased N content, C:P and N:P and decreased P content and C:N. At the community level, N content was lower and C:N higher in SR communities compared to CK. The N content of the plant community was positively correlated with soil total N content. S. chamaejasme removal could change the nutrient balance from species level, to functional group level, and to community level. Thus, supplementary measures might be cooperated with S. chamaejasme removal for the recovery of S. chamaejasme-dominated degraded grassland. These results provide insight into the role of S. chamaejasme in ecological protection and conservation, and the conclusions from this study could be used to develop effective and sustainable measures for S. chamaejasme control in the Qinghai-Tibetan Plateau.