Severe water deficit restricts biomass production of Lolium perenne L. and Trifolium repens L. and causes foliar nitrogen but not carbohydrate limitation

Abstract

Aims We investigated whether drought-induced impairment of grassland species can be explained directly by plant water deficit or by water-driven limitation of nitrogen (N) and/or carbohydrate sources. Methods In a field experiment, a severe drought treatment was applied on monocultures of Lolium perenne L. (cv. Alligator) (Lp) and Trifolium repens L. (cv. Hebe) (Tr) by using rainout shelters excluding all precipitation, and effects were compared to a rainfed control. Three species-fertiliser treatments were set up, crossed with the drought treatment. The two species were fertilised equally with N (200 kg N ha), and an additional high N fertilisation treatment was established for L. perenne (Lp highN , 500 kg N ha). Results Severe soil water deficit led to significantly lower leaf water potentials in all species-fertiliser treatments (P < 0.001) down to approximately −1.2 MPa and, on average, to a 79% reduction in living plant biomass above 7 cm harvest height (P < 0.001), indicating strong plant water deficits. Under the drought treatment, living plant biomass above 7 cm did not differ among species-fertiliser treatments. Plant-available soil N was 84% lower (P ≤ 0.01) and plant N concentrations were 24% less (P < 0.001) under the drought than under the rainfed control treatment, with Lp always being more N limited than Lp highN and Tr. Nitrate concentrations in water-limited plants were generally very low (< 0.85 mg g −1 dry matter), whereas non-structural carbohydrates were distinctly greater under the drought treatment in Lp (+62%), Lp highN (+46%), and Tr (+18%).Conclusions Restricted biomass production of these forage species under severe drought can primarily be explained by plant water deficits and secondarily by drought-induced limitation of N supply. However, growth seems not to be limited by carbohydrate source activity, as carbohydrates accumulated with water deficiency.

Timing of drought in the growing season and strong legacy effects determine the annual productivity of temperate grasses in a changing climate

“…In general, these studies have confirmed that a drought-induced water limitation typically leads to a reduction in net primary productivity (NPP;Fuchslueger et al, 2014Fuchslueger et al, , 2016Gherardi and Sala, 2019;Wilcox et al, 2017;Wu et al, 2011). Importantly, however, these studies have also shown that the response of ecosystems to experimental drought can vary quite dramatically (Gherardi and Sala, 2019;Gilgen and Buchmann, 2009;Grant et al, 2014;Hoover et al, 2014;Wilcox et al, 2017). Among others, the drought response of grasslands has been shown to depend on the severity of the experienced drought (Vicca et al, 2012;Wilcox et al, 2017) and important secondary factors, such as the type of grassland affected (Byrne et al, 2013;Gherardi and Sala, 2019;Sala et al, 2015;Wilcox et al, 2017), the intensity of land use (Vogel et al, 2012;Walter et al, 2012), the plant functional composition (Gherardi and Sala, 2015;Hofer et al, 2016Hofer et al, , 2017aMackie et al, 2018) or the biodiversity of an ecosystem (Haughey et al, 2018;Isbell et al, 2015;Kahmen et al, 2005;Wagg et al, 2017).…”

Timing of drought in the growing season and strong legacy effects determine the annual productivity of temperate grasses in a changing climate

“…Moreover, Arend et al (2016) found a rapid stimulation of photosynthesis immediately after rewetting that continued until the end of the growing season, partly compensating the loss of photosynthetic activity during drought. Hofer et al (2017b) found an increased root mass and increased water-soluble carbohydrate reserves in the stubbles of drought stressed L. perenne at the end of a drought stress period. Both of which could have contribute to increased growth rates observed in their study once rewetting had occurred.…”

“…Gutters were installed to prevent the water from flowing onto adjacent plots, and a 0.75 m boarder zone at each plot was not considered for measurements to prevent a possible effect of lateral water flow in the soil. These shelters and plot design had previously been successfully used in other grassland-drought experiments (Hofer et al, 2016(Hofer et al, , 2017a(Hofer et al, , 2017b. Rain-fed controls were subject to the natural precipitation regime.…”

“…The fact that inter-specific differences in the responses to the drought stress and to the following rewetted post-drought period in our study were smaller than in other studies, may be related to the fact that all six tested grasses belong to a relatively narrow functional group of productive fast-growing grasses with high demands for mineral N in the soil. The availability of mineral N in the soil was found to be a key factor for the response during as well as after drought for non-leguminous species (Hofer et al, 2017a(Hofer et al, , 2017b.…”

Soil Nitrogen Dynamics in a Managed Temperate Grassland Under Changed Climatic Conditions

“…In contrast, mineralization, nitrification, and denitrification were found to be lower under drier environmental conditions [23,24]. Droughts can cause a decrease in microbial biomass N and in N_PU in grasslands [25][26][27][28] and lower soil water content, both leading to a higher concentration of DIN in the soil solution [22]. The effects of drought periods followed by rewetting on the N-cycle vary [29].…”