Abstract: Agricultural practices enhancing soil organic carbon (SOC) show potential to buffer negative effects of climate change on forage grass performance. We tested this by subjecting five forage grass varieties differing in fodder quality and drought/flooding resistance to increased persistence in summer precipitation regimes (PR) across sandy and sandy-loam soils from either permanent (high SOC) or temporary grasslands (low SOC) in adjacent parcels. Over the course of two consecutive summers, monoculture mesocosms were subjected to rainy/dry weather alternation either every 3 days or every 30 days, whilst keeping total precipitation equal. Increased PR persistence induced species-specific drought damage and productivity declines. Soils from permanent grasslands with elevated SOC buffered plant quality, but buffering effects of SOC on drought damage, nutrient availability and yield differed between texture classes. In the more persistent PR, Festuca arundinacea FERMINA was the most productive species but had the lowest quality under both ample water supply and mild soil drought, whilst under the most intense soil droughts, Festulolium FESTILO maintained the highest yields. The hybrid Lolium × boucheanum kunth MELCOMBI had intermediate productivity and both Lolium perenne varieties showed the lowest yields under soil drought, but the highest forage quality (especially the tetraploid variety MELFORCE). Performance varied with plant maturity stage and across seasons/years and was driven by altered water and nutrient availability and related nitrogen nutrition among species during drought and upon rewetting. Moreover, whilst permanent grassland soils showed the most consistent positive effects on plant performance, their available water capacity also declined under increased PR persistence. We conclude that permanent grassland soils with historically elevated SOC likely buffer negative effects of increasing summer weather persistence on forage grass performance, but may also be more sensitive to degradation under climate change.

Abstract: Global warming is altering the intra-annual variability of precipitation patterns in the mid-latitudes, including a shift towards longer dry and wet spells compared to historic averages. Such fluctuations will likely alter soil water and nutrient dynamics of managed ecosystems which could negatively influence their functioning (e.g., productivity and fodder quality). Here, we investigated whether basalt addition could attenuate effects of increasingly persistent precipitation regimes (PR) on two agricultural grassland monocultures differing in drought resistance (low: Lolium perenne (LP) vs high: Festulolium (FL)) and digestibility (high: LP, low: FL), while improving soil C sequestration. In total, 32 experimental mesocosms were subjected to either a low (1-day wet/ dry alternation) or a highly (30-day wet/dry alternation) persistent PR over 120 days, keeping total precipitation equal. In half of these mesocosms, we mixed basalt with the top 20 cm soil layer at a rate of 50 t ha-1. Overall, 30-day PR increased average water availability resulting in improved aboveground biomass and shoot digestibility for both species, in spite of elevated physiological stress. These PR also increased shoot Si, K, N and C but reduced Ca accumulation. Basalt addition generally increased soil Al, Ni, Mg, Ca, P, K and Si availability without altering root biomass or total soil carbon. Moreover, differences in root N content and C:N ratio between species were reduced. Interestingly, basalt modified the PR effects on productivity. Within 30-day PR, basalt stimulated aboveground biomass (& PLUSMN;14%) and root Si and K contents without altering plant digestibility, palatability, crude protein content or Ni/Al content. These results indicate that basalt can stimulate grassland productivity and soil nutrient availability under more persistent PR without negatively affecting fodder quality. Hence, basalt application may improve the performance of young temperate grassland monocultures under climate change, though dry soil conditions may limit effects on soil C sequestration during summer.

Abstract: Climate models suggest that the persistence of summer precipitation regimes (PRs) is on the rise, characterized by both longer dry and longer wet durations. These PR changes may alter plant biochemical composition and thereby their economic and ecological characteristics. However, impacts of PR persistence have primarily been studied at the community level, largely ignoring the biochemistry of individual species. Here, we analyzed biochemical components of four grassland species with varying sensitivity to PR persistence (Holcus lanatus, Phleum pratense, Lychnis flos-cuculi, Plantago lanceolata) along a range of increasingly persistent PRs (longer consecutive dry and wet periods) in a mesocosm experiment. The more persistent PRs decreased nonstructural sugars, whereas they increased lignin in all species, possibly reducing plant quality. The most sensitive species Lychnis seemed less capable of altering its biochemical composition in response to altered PRs, which may partly explain its higher sensitivity. The more tolerant species may have a more robust and dynamic biochemical network, which buffers the effects of changes in individual biochemical components on biomass. We conclude that the biochemical composition changes are important determinants for plant performance under increasingly persistent precipitation regimes.