Screening optimal biomass source by assessing plant growth rate and water use efficiency on 21 woody species

Background/Question/Methods

Trees are an important source for sustaining ecosystem services, as well as providing biomass for cellulosic ethanol production. It is desirable to identify tree species that are especially efficient in the balance between water loss and carbon uptake. We used a common-garden approach to compare tree growth and water-use efficiency (WUE) for tree species at Energy Farm at Urbana, IL. Tree growth, leaf-level gas exchange, and leaf δ¹³C were measured on 21 tree species across growing season for two years.

Results/Conclusions

At the leaf level, species differed significantly in net assimilation rate (A_n), stomatal conductance (g_s), intrinsic WUE (WUE_gs, the ratio of A_n to g_s), integrated WUE (WUE_i, indicated by δ¹³C), but not in instaneous WUE (WUE_tr, the ratio of A_n to transpiration). WUE_i was positively correlated with WUE_gs, negatively correlated with specific leaf area (SLA), but not correlated with either A_n or WUE_tr.

At the tree level, Robinia pseudoacacia, Populus deltoides, Catalpa speciosa, Rhus copallinum, and Acer saccharinum had higher height and basal diameter growth than the other species. Growth rate was positively correlated with A_n, photosynthetic nitrogen use efficiency (PNUE) and negatively correlated with WUE_i, and had no relationship with WUE_gs, and WUE_tr.  Species differed in their strategy in nutrient and water use efficiency. The principle component analysis results indicated that among the fast growing species, Robinia pseudoacacia,  Catalpa speciosa, had relatively higher A_n, lower PNUE, WUE_i, WUEtr and WUE_gs, Rhus copallinum and Populus deltoids had averge WUE_i, higher A_n, PNUE, and WUE_tr, and Acer saccharinum had lower A_n, PNUE but higher SLA and WUE_gs.

The mismatch correlation between WUEi and WUEtr suggested that the evaporative demand in addition to stomatal conductance played an important role in affecting WUEtr. Higher carbon gain was not always coupled with lower WUE or higher PNUE. There is no strict trader-off between resource costs and carbon gains. Selecting tree species for biomass production should not based solely on either costs or benefits estimates.