Abstract
The grasslands on the semi-arid Loess Plateau of China are expected to be particularly responsive to the size and frequency changes of extreme precipitation events because their ecological processes are largely driven by distinct soil moisture pulses. However, the plant growth and competitiveness of co-dominant species in response to the changes in the amount and timing of soil water are still unclear. Thus, two co-dominant species, Bothriochloa ischaemum and Lespedeza davurica, were grown in seven mixture ratios under three watering regimes [80 ± 5% pot soil capacity (FC) (high watering), 60 ± 5% FC (moderate watering), and 40 ± 5% FC (low watering)] in a pot experiment. The soil water contents were rapidly improved from low to moderate water and from moderate to high water, respectively, at the heading, flowering, and maturity stages of B. ischaemum, and were maintained until the end of the growing season of each species. The biomass production of both species increased significantly with the increased soil water contents, particularly at the heading and flowering periods, with a more pronounced increase in B. ischaemum in the mixtures. The root/shoot ratio of both species was decreased when the soil water availability increased at the heading or flowering periods. The total biomass production, water use efficiency (WUE), and relative yield total (RYT) increased gradually with the increase of B. ischaemum in the mixtures. The relative competition intensity was below zero in B. ischaemum, and above zero in L. davurica. The competitive balance index calculated for B. ischaemum was increased with the increase of the soil water contents. Bothriochloa ischaemum responded more positively to the periodical increase in soil water availability than L. davurica, indicating that the abundance of B. ischaemum could increase in relatively wet seasons or plenty-rainfall periods. In addition, the mixture ratio of 10:2 (B. ischaemum to L. davurica) was the most compatible combination for the improved biomass production, WUE, and RYTs across all soil water treatments.
Highlights
Rainfall variability greatly affects the structure and function of ecosystems globally, especially in the arid and semi-arid regions (Knapp et al, 2003; Post and Knapp, 2020)
The total biomass production in each species was significantly increased as the proportion of B. ischaemum was increased in the mixture ratios, and the highest biomass production was at the 10:2 mixture ratio in most cases (Figure 2)
The curves of the replacement series diagrams of biomass production in B. ischaemum were concave, while those in L. davurica were convex, and their lines intersected to the left of the 6:6 mixture ratio, i.e., the proportion of B. ischaemum was lower in mixtures (Figure 2)
Summary
Rainfall variability greatly affects the structure and function of ecosystems globally, especially in the arid and semi-arid regions (Knapp et al, 2003; Post and Knapp, 2020). The response of the plant community to rainfall fluctuations is an integrative outcome from each species, the dominant species. The eco-physiological response of dominant species to the changes in rainfall pattern in the arid and semi-arid areas, depends on the capability of drought resistance in individual species, and on the ability to grow and recover after rainfalls, largely influenced by the antecedent soil water availability (Niu et al, 2016; Xiong et al, 2017). Intraspecific competition may replace interspecific facilitation as water stress is alleviated (GarcíaCervigón et al, 2013; Adler et al, 2018) Such shift in the competitive intensities and compensatory effect among species might be the key coexistence mechanism for stabilizing the grassland community productivity when encountering drought stress (Grant et al, 2014)
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