Quantifying nitrogen (N) constraints on terrestrial plant growth are critical for understanding the coupled carbon and N cycle and improving the accuracy of model simulation. Laboratory (lab) fertilization experiments are essential for understanding plant response to N addition in the field. However, field and lab experiments present differently on experimental conditions (e.g. temperature, water, light and nutrient) and N application pattern (dose, duration and frequency), which will regulate the effect of N on plant growth. Then large uncertainties might exist when we translate the results of N manipulative experiments from lab to field. Hence, through collecting data for responses of plant biomass to N addition from 1982-2017, we synthesized 121 field and 106 lab fertilization experiments to test (1) if plant growth responds differently to N addition between the lab and field fertilization experiments; (2) if yes, how the differences vary with plant growth forms and plant parts; (3) if the N application pattern or experimental condition regulate the differences.
Results/Conclusions
The results showed a general positive response of terrestrial plant growth to N addition both in lab (60.8%) and field (20.8%). However, threefold differences on plant growth existed between lab and field , and the differences varied with plant categories and plant parts. For example, the N–induced plant growth in the lab was about double as in the field for herbaceous (67.0% vs 28.8%) but fourfold for woody species (52.7% vs 11.7%). Furthermore, N-induced biomass was allocated more to above- (26.3%) in field, but equally to above- (61.1%) and below-ground (57.5%) biomass in lab. We found that as duration increasing and frequency decreasing, the difference of plant growth was gradually diminished. Furthermore, the difference was reduced under additional water but enlarged under phosphorus addition. Our results suggest that diverse environmental conditions (especially water and nutrient availability), and the additive N duration and frequency are the main reasons for the difference between lad and field response. It highlights more attention should be paid when we translate results of N manipulative experiments in the lab to the field.