Transpiration Rate of White Clover (Trifolium repens L.) Cultivars in Drying Soil.

Lucy Egan,Shirley Nichols,Rainer Hofmann,Valerio Hoyos-Villegas,Jonathan Hadipurnomo

doi:10.3389/fpls.2021.595030

Abstract

Determining the performance of white clover cultivars under drought conditions is critical in dry climates. However, comparing the differences in cultivar performance requires equivalent soil water content for all plants, to reduce the water deficit threshold eliciting stomatal closure. In this study, the objective was to compare the rate of stomatal closure in eighty white clover cultivars in response to soil drying. Two glasshouse experiments were conducted, and the daily transpiration rate was measured by weighing each pot. The transpiration rate of the drought-stressed plants were normalized against the control plants to minimize effects from transpiration fluctuations and was recorded as the normalized transpiration rate (NTR). The daily soil water content was expressed as the fraction of transpirable soil water (FTSW). The FTSW threshold (FTSWc) was estimated after which the NTR decreases linearly. The FTSWc marks the critical point where the stomata start to close, and transpiration decreases linearly. The significant difference (p < 0.05) between the 10 cultivars with the highest and lowest FTSWc demonstrates the cultivars would perform better in short- or long-term droughts.

Highlights

White clover is the most important pastoral legume in temperate regions of the world and is usually grown in companion with ryegrass (Caradus et al, 1989)
White clover is economically important to New Zealand and fixes approximately 1.57 million tons of nitrogen annually (Caradus et al, 1996)
This study aims to build on previous reports of FTSW critical threshold (FTSWc) in plant species (Sinclair and Ludlow, 1986; Weisz et al, 1994; Lecoeur and Sinclair, 1996; Ray and Sinclair, 1998; Gholipoor et al, 2013)

Summary

Introduction

White clover is the most important pastoral legume in temperate regions of the world and is usually grown in companion with ryegrass (Caradus et al, 1989). The pasture mix of ryegrass and white clover is common in a variety of grazing systems, including sheep and beef, deer, and dairy. White clover is an attractive plant to have in pastoral systems due to the nitrogen fixation ability and the resulting role in sustainable farming systems. White clover is economically important to New Zealand and fixes approximately 1.57 million tons of nitrogen annually (Caradus et al, 1996). New Zealand has the highest export share of white clover globally (57.5%), exporting approximately 4500 tons of white clover seed annually (Rattray, 2005). The domestic impact was ∼$1.5million and the export impact was Abbreviations: NTR, Normalized transpiration rate; FTSW, Fraction of transpirable soil water; VPD, Vapor pressure deficit; ISH, Interspecific hybrid

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