Variation in regrowth ability in relation to land-use intensity in three common grassland herbs

Abstract

Aims Plant populations in managed grasslands are subject to strong selection exerted by grazing, mowing and fertilization. Many previous studies showed that this can cause evolutionary changes in mean trait values, but little is known about the evolution of phenotypic plasticity in response to land use. In this study, we aimed to elucidate the relationships between phenotypic plasticity – specifically, regrowth ability after biomass removal – and the intensity of grassland management and levels of temporal variation therein. Methods We conducted an outdoor common garden experiment to test if plants from more intensively mown and grazed sites showed an increased ability to regrow after biomass removal. We used three common plant species from temperate European grasslands, with seed material from 58 – 68 populations along gradients of land-use intensity, ranging from extensive (only light grazing) to very intensive management (up to four cuts per year). Important findings In two out of three species, we found significant population differentiation in regrowth ability after clipping. While variation in regrowth ability was unrelated to the mean land-use intensity of populations of origin, we found a relationship with its temporal variation in P. lanceolata, where plants experiencing less variable environmental conditions over the last 11 years showed stronger regrowth in reproductive biomass after clipping. Therefore, while mean grazing and mowing intensity may not select for regrowth ability, the temporal stability of the environmental heterogeneity created by land use may have caused its evolution in some species.

Genetic variation in non-structural carbohydrates in Plantago lanceolata is related to mowing intensity but not to regrowth ability

“…However, when we related our NSC storage data with regrowth data from a sister study (Kirschbaum et al 2021) we found no relationship between the two. The role of NSCs for regrowth is still subject of debate.…”

“…Finally, we tested if relative NSC content was related to the regrowth ability of P. lanceolata after a clipping treatment. For this we used data from a common garden experiment with the same plant material where we had previously tested for plasticity of regrowth ability after a clipping treatment, and had calculated plasticity as the log response ratio of clipped versus unclipped plants in terms of their total and reproductive biomass at the end of the growing season (for details see Kirschbaum et al 2021). We fitted linear mixedeffects models with plasticity of total biomass of P. lanceolata as response variable, region of origin and flowering-corrected residuals of relative NSC content as fixed effects, and population as random effect.…”

“…For example, in perennial ryegrass, NSC significantly influenced early regrowth but after four weeks the NSC-biomass relationship had disappeared . As the regrowth ability in the current common garden study (Kirschbaum et al 2021) was evaluated 16 weeks after clipping, it is thus possible that we were unable to detect potential early correlations between NSC levels and regrowth ability. Moreover, NSCs may not be the only stored carbon compounds used for regrowth.…”

“…To investigate heritable variation in NSC content in the taproots of P. lanceolata we used the same seedlings as in an outdoor common garden experiment conducted from April-October seedling from five to seven seed families per population, altogether 370 plants. The procedures for sowing and germination (cold stratification), pots (1 L), soil type (sand-soil mixture), fertilization (equivalent of 60 kg N ha -1 ), watering (ad libitum but at least twice per week) and random placement on the field site were identical to the aforementioned common garden experiment (for details see Kirschbaum et al 2021). Six weeks after transplanting the seedlings to pots and placing them outside in our experimental garden, we recorded if plants flowered, measured rosette diameter as a proxy for plant size, and harvested belowground biomass for NSC analysis.…”

“…We also tested if pre-clipping levels of NSC positively affected the regrowth ability of P. lanceolata. For this, we used data from another common garden experiment, conducted with the same populations of P. lanceolata, in which we tested the effects of land-use intensity on the regrowth ability of P. lanceolata after a clipping treatment (Kirschbaum et al 2021). Specifically, we were interested in the following questions: 1) Is there genetic variation in the concentration of non-structural carbohydrates (NSCs) in P. lanceolata taproots along a land-use gradient?…”