Abstract
For a successful natural regeneration of Japanese white birch (Betula platyphylla var. japonica), competitive vegetation should be managed. Here, we clarified how soil water condition modifies the competitiveness of Japanese white birch against perennial weeds, Eupatorium species, based on an ecophysiological approach combining a glasshouse experiment and a field survey. We investigated photosynthetic and growth responses to various water regimes from water deficit to waterlogging (two times-a-week irrigation, three times-a-week irrigation, half waterlogging, and full waterlogging) in pot-grown seedlings of Japanese white birch and the competitive weed Eupatorium makinoi. The ratio of seedling height of Japanese white birch to seedling height of E. makinoi showed a decreasing trend from two times-a-week irrigation to full waterlogging, which suggests a lower competitiveness for light resource in Japanese white birch with increasing soil wetness. The maximum rate of Rubisco carboxylation (Vc,max) based on unit N was lower in waterlogging treatments than in two times- and three times-a-week irrigation in Japanese white birch, whereas E. makinoi showed the opposite response. This suggests that N partitioning into Rubisco and/or Rubisco activation might be suppressed in Japanese white birch but enhanced in E. makinoi under waterlogging. The maximum photochemical efficiency of photosystem II (Fv/Fm) was also lower in seedlings of Japanese white birch grown under waterlogging treatments. We further conducted a field survey on the relationship between Fv/Fm and topographic wetness index (TWI) in seedlings of Japanese white birch and E. glehnii (closely related to E. makinoi) naturally grown in a study site 5 years after canopy tree cutting. Lower Fv/Fm was observed in seedlings of Japanese white birch with increasing TWI, whereas no significant trend was observed in E. glehnii, in agreement with the glasshouse experiment. Thus, keeping soils not always humid might be favorable to photosynthetic performance and growth competitive ability of Japanese white birch against Eupatorium species.
Highlights
Japanese white birch (Betula platyphylla var. japonica) is a pioneer deciduous broadleaf tree species native to northern Japan, which naturally regenerates from anemochory seeds preferably in open habitats
The maximum photochemical efficiency of photosystem II (Fv/Fm) was lower in seedlings of Japanese white birch grown under waterlogging treatments
The most critical issue in the natural regeneration of Japanese white birch in northern Japan is the competition with other types of vegetation such as bonesets (Eupatorium makinoi, and E. glehnii), Sakhalin raspberry (Rubus matsumuranus), and sasa bamboo (e.g., Sasa senanensis)
Summary
Japanese white birch (Betula platyphylla var. japonica) is a pioneer deciduous broadleaf tree species native to northern Japan, which naturally regenerates from anemochory seeds preferably in open habitats. The most critical issue in the natural regeneration of Japanese white birch in northern Japan is the competition with other types of vegetation such as bonesets (Eupatorium makinoi, and E. glehnii), Sakhalin raspberry (Rubus matsumuranus), and sasa bamboo (e.g., Sasa senanensis). Sasa bamboo is a major competitor against birch regeneration, since sasa bamboo quickly occupies an open site with rhizomes, which creates a dense vegetation cover and a thick litter layer, which prevents germination and growth of light-demanding species such as Japanese white birch (Koike, 1988; Koike et al, 2001; Doležal et al, 2009; Seiwa et al, 2009). Soil scarification is expected to be an empirical treatment to promote Japanese white birch regeneration by removing rhizomes of sasa bamboo (Yamazaki and Yoshida, 2018, 2020). Even when rhizomes of sasa bamboo are successfully removed by scarification, other weed species would outcompete regenerating seedlings of Japanese white birch
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
