Interactive Effects Of Water Availability Research Articles

Experimental drought suppresses grass productivity and passive warming promotes tree sapling performance: Insights from African savanna species

Warming as well as increasingly frequent and severe droughts under climate change are expected to have global impacts on vegetation. We examined the independent and interactive effects of water availability and warming on the growth of savanna grasses and tree saplings. We used a widespread C4 grass species Eragrostis curvula, and a native woody encroacher, Vachellia sieberiana, in South Africa. We simulated a typical savanna microhabitat by planting tree species within a grass matrix, in 45 L containers. Watering treatments were applied weekly as drought (minus 40% of the long-term average), normal (same amount as the long-term average), and excess (addition of 40% of the long-term average). Passive warming was achieved using open-top chambers. We found that water availability was the main limiting factor for grass productivity, with low grass biomass attained under drought treatments. Warming had no significant effect on grass productivity, but had a large positive effect on tree sapling growth and performance when coupled with excess or normal water treatments. Tree sapling root: shoot ratios were highest in the drought treatment, possibly as an adaptation to low water-supply. Specific leaf area was higher with warming than ambient, further elucidating the positive effect of increased temperature for tree growth. Drought has important negative implications for grass productivity, and may reduce the competitive effects of grasses on trees, particularly during the early sapling stage, when competition for resources between tree saplings and grasses are maximised. Coupled with increased performance of trees under warmer conditions, future climate change may further promote tree establishment, especially in areas where rainfall is limiting.

Effects of mixing tree species and water availability on soil organic carbon stocks are depth dependent in a temperate podzol

AbstractMixing tree species is a forest management strategy put forward to increase and stabilize primary productivity. Yet, little is known about soil organic carbon (SOC) storage in mixed species forests, particularly under water shortage. In this study, we used a tree diversity experiment in southwestern France to assess the interactive effects of water availability (via irrigation) and mixing tree species (monocultures of pine (Pinus pinaster) and birch (Betula pendula) versus mixed plots of pine‐birch and pine‐birch‐oak (Quercus robur)) on SOC stocks in the forest floor and across five mineral soil layers (0–5, 5–15, 15–30, 30–60 and 60–90 cm deep). We found that SOC stocks were negatively affected by irrigation in the forest floor due to an increase in decomposition rates. However, SOC stocks were positively influenced by both the mixing of tree species and irrigation in the mineral soil, particularly at the 15–30‐cm soil depth. This is because root niche partitioning in mixed plots and an increase in tree biomass in irrigated plots may have resulted in greater organic matter inputs through rhizodeposition and the incorporation of microbially‐derived compounds. These preliminary results indicate that SOC dynamics and its response to biotic and abiotic factors are strongly dependent on soil depth. Our data further highlight that the positive effect of mixing trees on SOC stocks was higher in irrigated plots, thereby contradicting the idea that tree mixture effects are expected to be greater when environmental conditions are harsher. We conclude that mixing tree species can increase SOC stocks in the short term in temperate forests, even if the exact mechanisms remain to be identified.Highlights Effects of mixing trees and increasing water availability on SOC are depth dependent. Increase in SOC stocks occurred mainly at the mid‐soil depth (15–30 cm). Effects of tree mixture on SOC were greater when soil water availability was high.

Testing for loss of Epichloë and non-epichloid symbionts under altered rainfall regimes.

Microbial symbionts can buffer plant hosts from environmental change. Therefore, understanding how global change factors alter the associations between hosts and their microbial symbionts may improve predictions of future changes in host population dynamics and microbial diversity. Here, we investigated how one global change factor, precipitation, affected the maintenance or loss of symbiotic fungal endophytes in a C3 grass host. Specifically, we examined the distinct responses of Epichloë (vertically transmitted and systemic) and non-epichloid endophytes (typically horizontally transmitted and localized) by considering (1) how precipitation altered associations with Epichloë and non-epichloid endophytic taxa across host ontogeny, and (2) interactive effects of water availability and Epichloë on early seedling life history stages. We manipulated the presence of Epichloë amarillans in American beachgrass (Ammophila breviligulata) in a multiyear field experiment that imposed three precipitation regimes (ambient or ±30% rainfall). In laboratory assays, we investigated the interactive effects of water availability and Epichloë on seed viability and germination. Reduced precipitation decreased the incidence of Epichloë in leaves in the final sampling period, but had no effect on associations with non-epichloid taxa. Epichloë reduced the incidence of non-epichloid endophytes, including systemic p-endophytes, in seeds. Laboratory assays suggested that association with Epichloë is likely maintained, in part, due to increased seed viability and germination regardless of water availability. Our study empirically demonstrates several pathways for plant symbionts to be lost or maintained across host ontogeny and suggests that reductions in precipitation can drive the loss of a plant's microbial symbionts.

Effects of water availability and pest pressures on tea (Camellia sinensis) growth and functional quality.

Extreme shifts in water availability linked to global climate change are impacting crops worldwide. The present study examines the direct and interactive effects of water availability and pest pressures on tea (Camellia sinensis; Theaceae) growth and functional quality. Manipulative greenhouse experiments were used to measure the effects of variable water availability and pest pressures simulated by jasmonic acid (JA) on tea leaf growth and secondary metabolites that determine tea quality. Water treatments were simulated to replicate ideal tea growing conditions and extreme precipitation events in tropical southwestern China, a major centre of tea production. Results show that higher water availability and JA significantly increased the growth of new leaves while their interactive effect was not significant. The effect of water availability and JA on tea quality varied with individual secondary metabolites. Higher water availability significantly increased total methylxanthine concentrations of tea leaves but there was no significant effect of JA treatments or the interaction of water and JA. Water availability, JA treatments or their interactive effects had no effect on the concentrations of epigallocatechin 3-gallate. In contrast, increased water availability resulted in significantly lower concentrations of epicatechin 3-gallate but the effect of JA and the interactive effects of water and JA were not significant. Lastly, higher water availability resulted in significantly higher total phenolic concentrations but there was no significant impact of JA and their interaction. These findings point to the fascinating dynamics of climate change effects on tea plants with offsetting interactions between precipitation and pest pressures within agro-ecosystems, and the need for future climate studies to examine interactive biotic and abiotic effects.