Effects of Irrigation and Nitrogen Fertilization on Seed Yield, Yield Components, and Water Use Efficiency of Cleistogenes songorica

Irrigation and nitrogen (N) are two crucial factors affecting perennial grass seed production. To investigate the effects of irrigation and N rate on seed yield (SY), yield components, and water use efficiency (WUE) of Cleistogenes songorica (Roshevitz) Ohwi, an ecologically significant perennial grass, a four-year (2016–2019) field trial was conducted in an arid region of northwestern China. Two irrigation regimes (I1 treatment: irrigation at tillering stage; I2 treatment: irrigation at tillering, spikelet initiation, and early flowering stages) and four N rates (0, 60, 120, 180 kg ha−1) were arranged. Increasing amounts of both irrigation and N improved SY, evapotranspiration, WUE, and related yield components like fertile tillers m−2 (FTSM) and seeds spikelet−1. Meanwhile, no significant difference was observed between 120 and 180 kg N ha−1 treatments for most variables. The highest SY and WUE was obtained with treatment combination of I2 plus 120 kg N ha−1 with four-year average values of 507.3 kg ha−1 and 1.8 kg ha−1 mm−1, respectively. Path coefficient and contribution analysis indicated that FTSM was the most important yield component for SY, with direct path coefficient and contribution coefficient of 0.626 and 0.592. Overall, we recommend I2 treatment (three irrigations) together with 120 kg N ha−1 to both increase SY and WUE, especially in arid regions. Future agronomic managements and breeding programs for seed should mainly focus on FTSM. This study will enable grass seed producers, plant breeders, and government program directors to more effectively target higher SY of C. songorica

Effects of Irrigation and Nitrogen Fertilization on Seed Yield, Yield Components, and Water Use Efficiency of <i>Cleistogenes songorica</i>

Irrigation and nitrogen (N) are two crucial factors affecting perennial grass seed production. To investigate the effects of irrigation and N rate on seed yield (SY), yield components, and water use efficiency (WUE) of Cleistogenes songorica (Roshevitz) Ohwi, an ecologically significant perennial grass, a four-year (2016–2019) field trial was conducted in an arid region of northwestern China. Two irrigation regimes (I1 treatment: irrigation at tillering stage; I2 treatment: irrigation at tillering, spikelet initiation, and early flowering stages) and four N rates (0, 60, 120, 180 kg ha−1) were arranged. Increasing amounts of both irrigation and N improved SY, evapotranspiration, WUE, and related yield components like fertile tillers m−2 (FTSM) and seeds spikelet−1. Meanwhile, no significant difference was observed between 120 and 180 kg N ha−1 treatments for most variables. The highest SY and WUE was obtained with treatment combination of I2 plus 120 kg N ha−1 with four-year average values of 507.3 kg ha−1 and 1.8 kg ha−1 mm−1, respectively. Path coefficient and contribution analysis indicated that FTSM was the most important yield component for SY, with direct path coefficient and contribution coefficient of 0.626 and 0.592. Overall, we recommend I2 treatment (three irrigations) together with 120 kg N ha−1 to both increase SY and WUE, especially in arid regions. Future agronomic managements and breeding programs for seed should mainly focus on FTSM. This study will enable grass seed producers, plant breeders, and government program directors to more effectively target higher SY of C. songorica

<b>Local adaptation is highly dependent on common garden selection: evidence from a 7-year study on a dominant alpine meadows species</b>

1. Combining common garden experiments with reciprocal garden experiments is widely used to assess local adaptation in plants. This method effectively reduces the potential influence of the maternal environment derived from seed origin. However, the impact of divergent common garden environments on local adaptation assessment are still unknown.2. To examine the potential effects of common garden selection on local adaptation assessment, we conducted two-year common garden experiments followed by five-year reciprocal sowing experiments at low and high altitude sites. In each common garden, seeds of four Elymus nutans populations were directly sown to minimize maternal environment effect from seed origin and to generate seeds for subsequent reciprocal sowing experiments. We measured multiple traits in both experiments, including seedling emergence, survival, plant height, aboveground biomass, reproductive branch count, and the number of seeds per individual. This method allowed us to investigate variations in local adaptation across different growth years and life cycle stages.3. Our findings suggest that the low-altitude population exhibits local adaptation in the low-altitude reciprocal sowing garden. However, in the high-altitude reciprocal sowing garden, this adaptive advantage was only observed when seeds were obtained from the low-altitude common garden. Furthermore, our long-term experiment has revealed a gradual decrease in the adaptive advantage of E. nutans as growth year increase. Notably, this adaptive advantage is primarily observed in the number of seeds, with a relatively weaker local adaptation in seedling survival. No evidence of local adaptation is found in other traits.4. Synthesis and applications. The local adaptation of E. nutans is primarily exhibited during the early growth years and is highly dependent on common garden selection. Thus, for the assessment and selection of seed sources in ecological restoration projects, we recommend initially producing seeds in common gardens and subsequently conducting multi-year reciprocal garden experiments using these seeds. Moreover, the ecological restoration projects that involve E. nutans, giving priority to native or closely related populations would significantly enhances the long-term sustainability of degraded grassland.</p