Effects of Soil Water and Nitrogen on Growth and Photosynthetic Response of Manchurian Ash (Fraxinus mandshurica) Seedlings in Northeastern China

Soil water and nitrogen (N) are considered to be the main environmental factors limiting plant growth and photosynthetic capacity. However, less is known about the interactive effects of soil water and N on tree growth and photosynthetic response in the temperate ecosystem. seedlings. The seedlings were exposed to three water regimes including natural precipitation (CK), higher precipitation (HW) (CK +30%) and lower precipitation (LW) (CK −30%), and both with and without N addition for two growing seasons. We demonstrated that water and N supply led to a significant increase in the growth and biomass production of the seedlings. LW treatment significantly decreased biomass production and leaf N content, but they showed marked increases in N addition. N addition could enhance the photosynthetic capability under HW and CK conditions. Leaf chlorophyll content and the initial activity of Rubisco were dramatically increased by N addition regardless of soil water condition. The positive relationships were found between photosynthetic capacity, leaf N content, and SLA in response to water and N supply in the seedling. Rubisco expression was up-regulated by N addition with decreasing soil water content. Immunofluorescent staining showed that the labeling for Rubisco was relatively low in leaves of the seedlings under LW condition. The accumulation of Rubisco was increased in leaf tissues of LW by N addition. seedlings, which may provide novel insights on the potential responses of the forest ecosystem to climate change associated with increasing N deposition

Experimental influence of pH on the early life-stages of sea urchins II: increasing parental exposure times gives rise to different responses

Many studies into the responses of early life-stages to ocean acidification utilise offspring obtained from parents reared under present-day conditions. Their offspring are directly introduced to altered-pH conditions. This study determined whether this approach is suitable by pre-exposing parent sea urchins (Psammechinus miliaris) to altered seawater pH (~1000 μatm) for several durations, spawning them and rearing their offspring to settlement. Parents acclimated when exposed to low seawater pH for extended periods (>42 d). Longer adult pre-exposures reduced larval survival and less competent offspring were removed from populations earlier than in controls. Control offspring were larger during earlier development stages (2–7 d), but smaller during later development stages (14 + d) than offspring reared under low pH conditions. Juvenile settlement levels were similar across all treatments. After 17 d, offspring sourced from parents pre-exposed to low pH for 42 and 70 d were larger than those pre-exposed for 28 d and ambient sourced offspring directly transferred to low pH. These different responses show that the use of ambient derived offspring utilised in many studies is likely not an ideal approach when assessing larval development responses via morphometric measurements and survivorship prior to settlement. This study also suggests that calcifying organisms have capacities to acclimate and possibly adapt towards conditions beyond natural rates of ocean acidification