Effects of temporal heterogeneity of watering on size of an annual forb, Perilla frutescens (Lamiaceae), depend on soil nutrient levels

Abstract

Temporal heterogeneity of watering affects plant growth. When the same total amount of water is supplied, frequent watering leads to greater plant size than infrequent watering. However, the effects of a given watering regime can differ when nutrient levels vary. An experiment was designed to test the hypothesis that the effects of temporal heterogeneity of watering on plant growth also vary as a function of nutrient levels. Perilla frutescens (L.) Britton was grown using different combinations of nutrient levels and watering frequencies, with total water held constant across the treatments. The effects on plant size were analysed after 36 d. Under nutrient-rich conditions, frequent watering resulted in significantly larger plants than infrequent watering. However, under nutrient-poor conditions, no significant difference was detected between the different watering frequencies. The temporal heterogeneity of watering thus appears to have different effects on plant growth at different nutrient levels. Therefore, the watering heterogeneity should be examined with nutrients as unity, because the watering heterogeneity and nutrients affect plant growth in an interactive manner.

Effects of temporal heterogeneity of water supply and nutrient levels on plant biomass growth depend on the plant's relative size within its population

“…Water heterogeneity and nutrient level both affected pot yield independently, although in a previous study, the homogeneous water supply increased the biomass of individual P. frutescens plants, especially at a high nutrient level (Hagiwara et al 2008). Plants under nutrient-rich conditions are expected to grow larger and to be more sensitive to variability in soil moisture than those under nutrient-poor conditions because of their large demands for water (Stevens et al 2006).…”

“…Under natural conditions, it grows on the forest floor under canopy gaps in evergreen forests in Japan, reaching heights of 50-80 cm, and flowers from September to October (Iwatsuki et al 1993). Previous studies showed that P. frutescens responded to water heterogeneity, and that it can be a good model species for studies of responses to watering regimes (Hagiwara et al 2008(Hagiwara et al , 2010. Seeds of P. frutescens were obtained from the Atariya Seed Co. (Chiba, Japan).…”

“…3;T a b l e1). A homogeneous water supply is likely to improve plant growth because it permits stable water uptake (e.g., Fay et al 2003;Hagiwara et al 2008). However, a homogeneous supply could also limit nutrient uptake and growth owing to the small amount of water provided at each watering, because mobilization of nutrients to roots depends on both diffusion and mass flow (Larcher 2003).…”

“…In fact, several studies revealed a significant interaction between water amount and water heterogeneity (Novoplansky and Goldberg 2001;Lundholm and Larson 2003;Sher et al 2004;Maestre and Reynolds 2007). On the other hand, few studies of resource heterogeneity have investigated the interaction between water and nutrients (but see Maestre and Reynolds 2007;Hagiwara et al 2008Hagiwara et al , 2010. The integrated effects of water heterogeneity and nutrient amounts on plants should be examined simultaneously for two primary reasons.…”

Combined effects between temporal heterogeneity of water supply, nutrient level, and population density on biomass of four broadly distributed herbaceous species

“…Nutrient levels must be considered in the study of water heterogeneity for three reasons: (1) nutrient availability depends on water availability (Lambers et al 1998); (2) plants will be more sensitive to variability in water supply under nutrientrich than under nutrient-poor conditions, because they grow larger and require more water when nutrients are abundant (Goldberg and Novoplansky 1997;Stevens et al 2006); and (3) nutrient levels affect the root growth of plants (Fitter 1997), and this consequently can affect water uptake. In fact, an interactive effect of water heterogeneity and nutrient levels has been reported in the annual herbaceous species Perilla frutescens L. (Hagiwara et al 2008(Hagiwara et al , 2010. A few agricultural studies have also showed the interaction of water heterogeneity and nutrient levels (Silber et al 2003;Xu et al 2004).…”