Root and shoot phenology and root longevity of Norway spruce saplings grown at different soil temperatures

Tree roots comprise a huge carbon pool. Their dynamics are driven by environmental factors and thereby affected by climate change. We studied the effects of soil temperature on root and shoot phenology and their linkages in Norway spruce (Picea abies (L.) Karst.). Saplings were grown in controlled-environment rooms for three simulated growing seasons (GS1, GS2, and GS3). Soil-temperature treatments of 9, 13, 18, and 21 °C were applied during GS2. Root growth was monitored with minirhizotrons and commenced in all treatments simultaneously. Temporal growth patterns of short and long roots were usually bimodal. Root growth was very low during the coldest treatment of GS2 but increased during GS3 as an aftereffect. During GS3, growth of short roots continued later after colder treatments than warmer treatments. Reduced sink strength of roots and increased carbohydrate accumulation into needles at 9 °C during GS2 probably enabled compensatory root growth under restored temperatures during GS3. Soil temperature did not affect shoot phenology, and root and shoot phenology varied between growing seasons; thus, the linkage of root and shoot phenology was inconsistent. In warmer soil, root longevity was shorter and turnover rate was higher than in colder soil. This can further affect soil carbon dynamics and ecosystem carbon cycling in boreal forest ecosystems.

Root distribution and demography in an avocado (Persea americana) orchard under groundcover management systems

The effect of groundcover management systems on root demography and distribution of newly planted avocado (Persea americana Mill) trees was examined using minirhizotron techniques. We evaluated three groundcover systems: (1) bare soil (BS), pre- and post-emergence herbicides; (2) vegetation strip (VS), post-emergence herbicide applied in a 1-m wide strip centred on the tree row plus a groundcover mixture seeded between tree rows; and (3) complete groundcover (GC), covering the entire surface of the plots. Root production was higher in the non-bearing year (2009–10) than in the bearing year (2010–11). Trees in the BS plots had more roots of bigger diameter in the top 30 cm of soil and trees in VS and GC plots had more roots in the 30–60 cm depth and of smaller diameter. Lifespan of spring-born roots were 61 and 59% greater than those born during autumn and summer, respectively and soil depth and root diameter were positively correlated with root longevity. Lifespan of thinner roots (<0.2 mm) in the BS and VS plots were 49 and 33% greater than GC respectively. Avocado trees grown in contrasting condition compared with their native habitat show high morphological root plasticity, in response to resource and non-resource competition when grown in mixed stands.