Ethylenediurea (EDU) spray effects on willows (Salix sachalinensis F. Schmid) grown in ambient or ozone-enriched air: implications for renewable biomass production

Ground-level ozone (O3) is a widespread air pollutant causing extensive injuries in plants. However, its effects on perennial energy crops remain poorly understood due to technical difficulties in cultivating fast-growing shrubs for biomass production under O3 treatment on the field. Here we present the results of a two-year evaluation in the framework of which willow (Salix sachalinensis F. Schmid) shrubs were exposed to ambient (AOZ) or elevated (EOZ) O3 in two successive growing seasons (2014, 2015) and treated with 0 (EDU0) or 400 mg L−1 (EDU400) ethylenediurea spray in the second growing season. In 2014, EOZ altered the chemical composition of both top young and fallen leaves, and a novel mechanism of decreasing Mg in fallen leaves while highly enriching it in young top leaves was revealed in shrubs exposed to EOZ. In 2015, EDU400 alleviated EOZ-induced decreases in leaf fresh mass to dry mass ratio (FM/DM) and leaf mass per area (LMA). While EDU400 protected against EOZ-induced suppression of the maximum rate at which leaves can fix carbon (Amax) in O3-asymptomatic leaves, it did not alleviate EOZ-induced suppression of the maximum rates of carboxylation (VCmax) and electron transport (Jmax) and chlorophylls a, b, and a + b in the same type of leaves. In O3-symptomatic leaves, however, EDU400 alleviated EOZ-induced suppression of chlorophylls a and a + b, indicating different mode of action of EDU between O3-asymptomatic and O3-symptomatic leaves. Extensive herbivory occurred only in AOZ-exposed plants, leading to suppressed biomass production, while EOZ also led to a similar suppression of biomass production (EDU0 × EOZ vs. EDU400 × EOZ). In 2016, carry-over effects were also evaluated following cropping and transplantation into new ambient plots. Effects of EOZ in the preceding growing seasons extended to the third growing season in the form of suppressed ratoon biomass production, indicating carry-over effect of EOZ. Although EDU400 protected against EOZ-induced suppression of biomass production when applied in 2015, there was no carry-over effect of EDU in the absence of EDU treatment in 2016. The results of this study provide novel mechanistic understandings of O3 and EDU modes of action and can enlighten cultivation of willow as energy crop.

Effects of different foliar nitrogen fertilizers on cellular nitrogen metabolism and biomass of two shrub willow cultivars

We examined the effects of foliar supplementation of different nitrogen sources (urea, Nitamin, NH4NO3, and arginine) to study their efficacy as fertilizers for growth of two clonally propagated shrub willow cultivars; namely, ‘Fish Creek’ (Salix purpurea L.) and ‘Preble’ (Salix viminalis L. × (Salix sachalinensis F. Schmidt × Salix miyabeana Seemen)). Our objectives were to determine (i) if foliar nitrogen application is an effective method of fertilization for the two shrub willows and (ii) if different nitrogen sources are metabolized similarly by the plants. The analyses involved soluble leaf polyamines, amino acids, total protein, total nitrogen and carbon, and plant biomass in response to short-term treatments with four sources of nitrogen. The effects of foliar nitrogen application on leaf chemistry, biomass, and foliar nitrogen content varied according to the form of nitrogen used. The data indicate that (i) urea is the most suitable nitrogen source for foliar spray (29% higher N accumulation vs. Nitamin), whereas arginine is the least suitable, and (ii) different nitrogen sources are metabolized differently by the plant. While the foliar nitrogen application method could become a practical and sustainable way to fertilize shrub willows and other short-rotation biofuel crops, it may also help reduce nitrogen loss to the environment.

Sexual differences in shoot and leaf dynamics in the dioecious tree Salix sachalinensis

In the dioecious tree Salix sachalinensis Fr. Schm., females invested a greater amount of biomass to reproductive organs compared with males, indicating a greater reproductive cost in females. To elucidate mechanisms for the compensation of reproductive costs in females, we examined differences between the sexes in resource allocation, leaf and shoot dynamics, and leaf photosynthetic ability. In individual 1-year-old shoots, greater vegetative shoot biomass was observed in females than in males, although the mean mass of individual vegetative shoots was lower in females than in males. In both sexes, vegetative shoots at the proximal end of 1-year-old shoots completed their annual leaf production earliest and began shedding leaves earliest, although the light conditions did not differ from those at the terminal end. The leaf and shoot structure and dynamics in S. sachalinensis suggest effective carbon gain for both sexes by always placing new leaves with high photosynthetic rates at terminal shoot positions. In females, in particular, the net carbon gain would be increased by reducing construction and respiration costs and tissue loss by placing inexpensive small shoots in proximal shoot positions. To investigate to what extent the photosynthetic capacity of short-lived shoots compensated for reproductive costs in females, 80% of the vegetative-shoot buds were removed from 1-year-old shoots in females and males to simulate natural shoot shedding. In the current year, shoot removal did not reduce reproductive investment, but strongly reduced the diameter growth of 1-year-old shoots, in which the reduction was much greater in females than in males. In the following year, a reduction in reproductive investment was observed in females. Females of S. sachalinensis compensated for reproductive costs, not only by investing a greater amount of biomass in vegetative shoots, but also by using a more effective system of carbon acquisition (rapid leaf turnover on inexpensive shoots) than males.

SOME PROPERTIES OF THE BACTERIAL WETWOOD (WATERMARK) IN SALIX SACHALINENSIS CAUSED BY ERWINIA SALICIS

Some properties of bacterial wetwood (watermark) in Salix sachalinensis caused by Erwinia salicis were investigated. Vessel-ray parenchyma and interfibre pit membranes were often damaged or absent. Hence, they could serve as effective pathways for water transport resulting in water accumulation. Osmotic potentials (φπ) were substantially lower than those in healthy sapwood. 13C-NMR spectroscopy revealed that E. salicis produced levan in the watermark, which is suspected to be a causal agent of low φπ. These data support the concept that levan production decreases φπ, leading to water accumulation.