Temporal variation and its drivers in the elemental traits of four boreal plant species

Aims Intraspecific variation in plant traits has important consequences for individual fitness and herbivore foraging. For plants, trait variability across spatial dimensions is well documented. However, temporal dimensions of trait variability are less well known, and may be influenced by seasonal differences in growing degree days, temperature, and precipitation. Here, we aim to quantify intraspecific temporal variation in traits and the underlying drivers for four commonly occurring boreal plant species. Methods We sampled the elemental and stoichiometric traits (%C, %N, %P, C:N, C:P, N:P) of four common browse species’ foliage across two years. Using a two-step approach, we first fitted generalized linear models (GzLM, n = 24) to the species’ elemental and stoichiometric traits, and tested if they varied across years. When we observed evidence for temporal variability, we fitted a second set of GzLMs (n = 8) with temperature, productivity, and moisture as explanatory variables. Important Findings We found no evidence of temporal variation for most of the elemental and stoichiometric traits of our four boreal plants, with two exceptions. Year was an important predictor for percent carbon across all four species (R 2 = 0.47 to 0.67) and for multiple elemental and stoichiometric traits in balsam fir (5/8, R 2 = 0.29 to 0.67). Thus, variation in percent carbon was related to interannual differences, more so than nitrogen and phosphorus, which are limiting nutrients in the boreal forest. These results also indicate that year may explain more variation in conifers’ stoichiometry than for deciduous plants due to life history differences. Growing degree days (GDD) was the most frequently occurring variable in the second round of models (8/8 times, R 2 = 0.21 to 0.41), suggesting that temperature is an important driver of temporal variation in these traits.

Dynamics in Stoichiometric Traits and Carbon, Nitrogen, and Phosphorus Pools across Three Different-Aged Picea asperata Mast. Plantations on the Eastern Tibet Plateau

Understanding the variations in soil and plants with stand aging is important for improving management measures to promote the sustainable development of plantations. However, few studies have been conducted on the dynamics of stoichiometric traits and carbon (C), nitrogen (N), and phosphorus (P) pools across Picea asperata Mast plantations of different ages in subalpine regions. In the present study, we examined the stoichiometric traits and C, N, and P stocks in different components of three different aged (22-, 32-, and 42-year-old) P. asperata plantations by plot-level inventories. We hypothesized that the stoichiometric traits in mineral soil could shape the corresponding stoichiometric traits in soil microbes, tree roots and foliage, and the C, N, and P stocks of the total P. asperata plantation ecosystem would increase with increasing stand age. Our results show that the N:P ratio in mineral soil was significantly correlated with that in tree foliage and herbs. Additionally, the C:N ratio and C:P ratio in mineral soil only correlated with the corresponding stoichiometric traits in soil microbes and forest floor, respectively. Both the fractions of microbial biomass C in soil organic C and microbial biomass N in soil total N decreased with increasing stand age. The C, N, and P stocks of the total ecosystem did not continuously increase across stand development. In particular, the P stock of the total ecosystem exhibited a trend of increasing first and then decreasing. The aboveground tree biomass C accounted for more than 55% of the total ecosystem C stock regardless of stand age. In contrast, mineral soil and forest floor were the major contributors to the total ecosystem N and P stocks in all stands. This study suggested that all three different stands were N limited, and the stoichiometric homeostasis in the roots of P. asperata was more stable than that in the foliage. In addition, the soil microbial community assembly may change with increasing stand age for P. asperata plantations in the subalpine region.

Variation of morphological and leaf stoichiometric traits of two endemic species along the elevation gradient of Mount Kenya, East Africa

Aims The aim of this paper is to assess morphological and leaf stoichiometric responses of Dendrosenecio keniensis and Lobelia gregoriana to extreme environmental conditions along an elevation gradient in tropical mountains. Methods In this study, we assessed the variation of the morphological traits, including plant height, leaf area, leaf thickness, leaf dry weight, specific leaf area and the leaf stoichiometry traits nitrogen, carbon and phosphorous of the two endemic species D. keniensis and L. gregoriana. We further explored the relations of these morphological traits to soil organic carbon, soil total nitrogen, soil phosphorous, annual mean temperature, annual mean precipitation, annual total solar radiation, water vapor pressure and the topographic variables aspect, slope and hill shade along the elevation gradient. Ninety 10 m × 10 m sampling plots were set up along the elevation gradient ranging from 3500 to 4300 m. We used 1 km × 1 km grid cells to rasterize our study area in ArcGIS 10.5 for easy access to data pertaining to the climate of each elevation band. We performed linear regression of the morphological and leaf stoichiometric traits with elevation as explanatory variable. We conducted correlation analysis on the morphological and leaf stoichiometric traits with climatic, soil and topographic variables along the elevation gradient. Important Findings Dendrosenecio keniensis had wool-like pubescent leaves while L. gregoriana had mucilage packed succulent and waxy cuticle leaves to avoid freezing. Both species exhibited reduced metabolic rates as shown by the low leaf phosphorous content. Our results also showed that changes in morphology and leaf stoichiometry were determined by a combination of climate, soil and topographic variables that change along elevation on Mount Kenya. The observed variations in the morphological and leaf stoichiometric traits of D. keniensis and L. gregoriana, which grow side by side along the elevation gradient, were interpreted as adaptation to the harsh environmental conditions.