The objective of this paper is to clarify the effects of multiple environmental conditions, elevated atmospheric CO2 concentration ([CO2]) and soil conditions on the physiological and morphological properties of Alnus hirsuta Turcz., an N2-fixing species, to predict its responses to environmental changes. We examined the responses of photosynthetic properties, leaf characteristics, biomass and N allocation of A. hirsuta to elevated [CO2], soil N and phosphorus availability, and soil drought by using the results of two experiments. The effects of P availability were more marked than those of N availability and soil drought. The photosynthetic responses of A. hirsuta to elevated [CO2] under high P were considered to be ‘photosynthetic acclimation’, while A. hirsuta presented the obvious ‘photosynthetic downregulation’ to elevated [CO2] under low P. Soil P availability affected the growth responses to elevated [CO2] through effects on these photosynthetic properties and biomass allocation. Though elevated [CO2] caused no marked change in the allometric relationships in biomass, with some exceptions, the responses of N allocation among tissue to elevated [CO2] differed from those of biomass allocation. These results suggest that it is necessary to evaluate N mass allocation as well as biomass when we consider the N2-fixing ability of Alnus under elevated [CO2].

A previous study revealed low survival rates for Japanese larch (Larix kaempferi) summer-planted seedlings grown in Hiko-V-120 containers. This study examines nursery practices that could potentially prevent deterioration of the seedling water balance after planting to improve the survival rate of this species, which has a low drought tolerance. During summer planting, we tested (1) drought hardening or high-potassium fertilization for two months before planting, (2) antitranspirant or topping treatment at planting, and (3) the use of the JFA-150 container with a larger capacity and lower growing density than the Hiko-V-120 container. Drought hardening increased seedling drought tolerance because of the low leaf:root ratio, due to lower leaf mass production, resulting in increased survival from 74% to 93% in Hiko-V-120 containers. When JFA-150 containers were used, the leaf:root ratio was lower because of higher root mass, resulting in an increase in survival to 87%, with the highest survival of 97% when combined with drought hardening. The application of antitranspirant increased survival to over 90%, whereas topping did not, probably because of severer competition from weeds. High-potassium fertilization did not affect seedling traits or survival. For better survival of summer-planted container-grown Japanese larch seedlings, it is recommended that they be grown in containers providing sufficient cell volume and density for root growth while the seedlings are in the nursery and that irrigation be withheld for two months before planting. In addition, to obtain higher survival, an antitranspirant can be applied at planting at a cost.