Spatial pattern and process at the plant neighbourhood scale: insights from communities dominated by the clonal grass Elymus repens (L.) Gould

Question: How do clonal traits of a locally dominant grass (Elymus repens (L.) Gould.) respond to soil heterogeneity and shape spatial patterns of its tillers? How do tiller spatial patterns constrain seedling recruitment within the community? Locations: Artificial banks of the River Rhône, France. Material and Methods: We examined 45 vegetation patches dominated by Elymus repens. During a first phase we tested relationships between soil variables and three clonal traits (spacer length, number of clumping tillers and branching rate), and between the same clonal traits and spatial patterns (i.e. density and degree of spatial aggregation) of tillers at a very fine scale. During a second phase, we performed a sowing experiment to investigate effects of density and spatial patterns of E. repens on recruitment of eight species selected from the regional species pool. Results: Clonal traits had clear effects – especially spacer length – on densification and aggregation of E. repens tillers and, at the same time, a clear response of these same clonal traits as soil granulometry changed. The density and degree of aggregation of E. repens tillers was positively correlated to total seedling cover and diversity at the finest spatial scales. Conclusions: Spatial patterning of a dominant perennial grass responds to soil heterogeneity through modifications of its clonal morphology as a trade‐off between phalanx and guerrilla forms. In turn, spatial patterns have strong effects on abundance and diversity of seedlings. Spatial patterns of tillers most probably led to formation of endogenous gaps in which the recruitment of new plant individuals was enhanced. Interestingly, we also observed more idiosyncratic effects of tiller spatial patterns on seedling cover and diversity when focusing on different growth forms of the sown species.     

Influence of boron on the reproductive growth of white clover (Trifolium repens L.) cultivars

The effect of boron on the reproductive growth of four contrasting white clover cultivars was examined in a controlled environment and glasshouse experiment. Plants grown under a nutrient regime excluding boron and those receiving 0.5 mg/litre boron had fewer stolons, reproductive stolons and inflorescences than those receiving 1, 2 or 3 mg/litre. Inflorescences were also smaller and had fewer seeds per floret. A boron concentration of 1 mg/litre gave optimum reproductive growth, higher levels of boron giving no further increase. Peduncle length and nectar quantity, but not nectar quality, were also influenced by boron indicating a possible beneficial effect of this element on pollinator activity. Cultivars differed in both vegetative and reproductive growth. Cv. Gwenda, a small leaved cultivar, had more stolons but fewer inflorescences than cv. Menna and smaller inflorescences than cv. Olwen, a large leaved cultivar. Generally, these cultivars responded similarly to boron. The implications of these results for the reproductive growth of white clover are discussed.