Effects of Phosphorus on Shoot and Root Growth, Partitioning, and Phosphorus Utilization Efficiency in Lantana

This study was undertaken to critically analyze the effects of reduced phosphorus (P) on shoot and root growth, partitioning, and phosphorus utilization efficiency (PUtE) in lantana (Lantana camara ‘New Gold’). Plants were grown in a 1:1 mixture of perlite and vermiculite with complete nutrient solutions containing a range of P concentrations considered to be deficient (1 mg·L−1), low (3 and 5 mg·L−1), adequate (10 mg·L−1), and high (20 and 30 mg·L−1). Higher P supply had most dramatic effect on increasing the number of leaves and leaf surface area, subsequently leading to a disproportionate increase in shoot biomass than root biomass. Increasing P from 1 to 30 mg·L−1 linearly (P < 0.0001) increased shoot dry weight (DW) during vegetative growth, and logarithmically (P < 0.0001) during reproductive growth. Regardless of plant growth stage, biomass of roots and flowers (inflorescences) logarithmically increased (P < 0.0001) with increasing P concentrations. Plants grown with lower P allocated more biomass to roots than shoots, resulting in a higher root-to-shoot ratio. Increasing P concentration to 20 mg·L−1 increased the accumulation of P in all plant parts, but predominantly in shoots, whereas further increasing the concentration increased the accumulation primarily in roots and flowers. Higher P accumulation in plant tissues did not strongly contribute to the biomass production. Phosphorus utilization efficiency was higher with lower P supply in all plant tissues. P-deficient roots had the highest PUtE and specific root length (SRL), and retained higher proportion of P compared with nondeficient roots. Our results indicate that P concentration at 20 mg·L−1 is sufficient to maintain optimal vegetative growth while reproductive growth does not require P concentrations over 10 mg·L−1 as it stimulates greater level of P accumulation in plant parts with little or no effect on growth and flowering, and biomass accumulation in lantana.

Temporal variability of size–growth relationships in a Norway spruce forest: the influences of stand structure, logging, and climate

In a forest stand, competition plays a central role, affecting individual growth. The size–growth relationship (SGR) indicates whether large trees grow proportionally more than (asymmetric SGR), equal to (symmetric), or less than (inversely asymmetric) smaller trees. SGR is thus an indicator of the growth partitioning and competition intensity within a stand. Using tree-ring analysis, we investigated long-term trends and interannual variability of SGR in several Norway spruce (Picea abies (L.) Karst.) stands in the Paneveggio Forest (eastern Italian Alps) over a 100-year period. The study plots were characterized by different stand structures (one multilayered and two monolayered) and disturbance histories (different dates of logging). Logging conducted until the 1940s induced an inversely asymmetric SGR in all the plots. During the successive five decades, in the monolayered plots, it shifted to direct asymmetric (plot 1) and to symmetric (plot 2). In the multilayered plot (plot 3), SGR remained inversely asymmetric. A direct effect of climate on SGR interannual variability was not found. However, fast-growing trees had a stronger climatic signal than slow-growing trees, indicating that growth rate affects tree response to climate. Moreover, we observed that sensitivity to climate was reduced in the monolayered plots over the study period, possibly as a consequence of increased competition.