Abstract
Both competition and burial are important factors that influence plant growth and structuring plant communities. Competition intensity may decline with increased burial stress. However, experimental evidence is scarce. The aim of this study was to elucidate the role of burial stress in influencing plant competition by investigating biomass accumulation, biomass allocation, and clonal growth performance of Carex brevicuspis, one of the dominant species in the Dongting Lake wetland in China. The experiment was conducted with two typical wetland species, C. brevicuspis (target plant) and Polygonum hydropiper (neighbor plant), in a target-neighbor design containing three densities (0, 199, and 398 neighbor plants m-2) and two burial depths (0 and 12 cm). The biomass accumulation of C. brevicuspis decreased with increment of P. hydropiper density in the 0 cm burial treatment. However, in the 12 cm burial treatment, biomass accumulation of C. brevicuspis did not change under medium and high P. hydropiper densities. The relative neighbor effect index (RNE) increased with enhancement of P. hydropiper density but decreased with increasing burial depth. The shoot mass fraction decreased with P. hydropiper density in the 12 cm burial treatments, but the root mass fraction was only affected by burial depth. However, the rhizome mass fraction increased with both P. hydropiper density and burial depth. The number of ramets decreased with increasing P. hydropiper density. With increasing burial depth and density, the proportion of spreading ramets increased from 34.23% to 80.44%, whereas that of clumping ramets decreased from 65.77% to 19.56%. Moreover, increased P. hydropiper density and burial depth led to greater spacer length. These data indicate that the competitive effect of P. hydropiper on C. brevicuspis was reduced by sand burial, which was reflected by different patterns of biomass accumulation and RNE at the two burial depth treatments. A change from a phalanx to a guerrilla growth form and spacer elongation induced by sand burial helped C. brevicuspis to acclimate to competition.
Highlights
Interactions among species, including competitive, neutral, and positive relationships, play a major role in structuring plant communities [1, 2]
P. hydropiper density had a significant effect on C. brevicuspis biomass accumulation (Table 1; Fig 2), which was highest in the 0 cm burial + no plant treatment (22.4 ± 1.3 g per plant) and lowest in the 0 cm burial + high density treatment (8.5 ± 0.6 g per plant)
Another study found no significant influence of burial depth on the growth performance of C. brevicuspis [17]
Summary
Interactions among species, including competitive, neutral, and positive relationships, play a major role in structuring plant communities [1, 2]. According to the stress-gradient hypothesis (SGH), the net negative competitive effects are more important under relatively benign environmental conditions, whereas positive facilitative effects are more important under harsher conditions [4,5,6]. Many other studies, including those conducted in the northwestern Negev desert of Israel and semi-arid Mediterranean steppes, have been failed to find support for this hypothesis [3, 7,8,9]. It seems that this divergence might account for differences in ecological factors (e.g., ecosystem types, stress intensities and stress types) and species traits [10]. Few studies have examined the relationship between competition and burial stress, which is a common stress in several types of wetlands, including coastal areas, river-connected lakes, and floodplains [13,14]
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