The resistance to waterlogging of three Eucalyptus species

On-farm assessment of eucalypt yield gaps - a case study for the producing areas of the state of Minas Gerais, Brazil

The concept of yield gaps provides a basis for identifying the main sources of production losses, caused by water or management deficiencies, which may help foresters and forest companies to better plan and make decisions in their areas. Thus, the aim of this study was to identify the magnitude and the major causes of yield gaps of eucalypts, being this the most planted forest genus in Brazil, in different producing regions of the state of Minas Gerais that has the largest planted area. To these ends, potential (Yp) and attainable (Ya) yields were simulated using the agroecological zone model (AEZ-FAO) adapted and calibrated for Brazilian eucalypt clones. Actual yield (Yr) data were obtained from 22 sites located in the state of Minas Gerais from 2009 to 2016, considering an average forest rotation of 6.7 years and plantings occurring between 2002 and 2010. From this, the total yield gap (YGtot), yield gap by water deficit (YGwd), and yield gap by sub-optimal management (YGman) were determined. The YGwd ranged from 37 to 69 m³ ha^-1 year^-1 across the 22 sites assessed, with an average value of 55 m³ ha^-1 year^-1. On the other hand, the YGman ranged from zero (optimal management) to 31 m³ ha^-1 year^-1. The eucalypt yield gap in commercial areas of Minas Gerais state was mainly caused by water deficit, which represented 77% of the total yield gap. On the other hand, the deficiencies in forest management accounted for 23% of the total yield gap.

Species and clonal variation in growth responses to waterlogging and submersion in the genus Salix

The responses of clones of a range of willow species to waterlogging and total submersion were compared in glasshouse experiments using specially constructed perspex tanks. Up to 13 weeks of waterlogging had little effect on form and growth rates of above-ground parts of two clones of Salix caprea L. and one clone of S. cinerea L. A second clone of S. cinerea responded differently to the other three clones by significantly increasing its leaf area and stem dry weight, suggesting that it is likely to be more tolerant of waterlogging.

Plant parts below the waterline in the waterlogging treatment responded very differently to the same parts on control plants. All waterlogged plants developed hypertrophied lenticels within four weeks, followed by significant increases in stem diameter. In each clone most of the pre-existing root system died by the end of the waterlogging treatment. All clones formed adventitious roots which varied considerably between the species and to a lesser extent between clones within each species. In S. cinerea many short, fine, much-branched roots grew vertically upwards until they reached the water surface. In S. cinerea clone 90 they originated from both the pre-existing woody roots and from the hypertrophied lenticels on the submerged portions of the stems. In S. cinerea clone 12 they developed only from the hypertrophied lenticels. New roots produced by waterlogged S. caprea clones were long, sparsely branched and floated on or near the surface of the water. As in S. cinerea clone 90 they originated from both the pre-existing woody roots and the submerged hypertrophied lenticels. Whereas roots of the control plants of all clones were mostly ectomycorrhizal, those of the waterlogged plants had no mycorrhizae. In a second waterlogging experiment S. × sericans, S. viminalis and S. fragilis produced adventitious roots more like those of S. caprea than S. cinerea. Plants of all clones removed from the waterlogging treatment after 16 days and kept with their soil at field capacity thereafter produced many new roots from their old root balls. After 32 days waterlogging no such recovery occurred.

Total submersion caused much more severe damage to the aerial parts of all tested species than waterlogging. After eight days submersion the shoot tips of S. fragilis were beginning to rot and by day 25 those of S. × sericans and S. viminalis were rotting too. Subsequently shoots developed from axillary buds which remained unaffected by rot throughout the experiment. In S. cinerea shoot growth ceased after eight days and terminal buds were formed which remained dormant but healthy throughout the experiment. Submersion caused progressive loss of pre-existing leaves in all species. Some newly formed leaves of each species developed epinastic deformities after > 16 days of submersion. All species except S. cinerea showed significant reductions in root dry weight after 32 days of submersion.

In a second submersion experiment responses of three clones each of S. purpurea and S. viminalis were compared. Shoot growth was reduced significantly in four of the six clones after 14 days. No further reductions occurred in the next 14 days of submersion. Root dry weight also decreased, but it took 28 days of submersion to produce the greatest effect. The faster growing clones of each species were more adversely affected by submersion in terms of both reduced shoot growth and root growth than those which grew more slowly.

Considerable intraspecific variability in responses to waterlogging and submersion have been shown in these experiments by clones not selected for their variation in flooding tolerance. This suggests that selection and breeding could lead to the development of flood-tolerant cultivars of species such as S. cinerea and S. caprea which are not noted for their ability to withstand inundation.

Recovery of kiwifruit vines from transient waterlogging of the root system

The extent to which kiwifruit vines (Actinidia deliciosa var. deliciosa) recovered from transient waterlogging of the root system was determined under controlled conditions. Vines were waterlogged for periods varying from 1 to 7 days. The effects of decreasing concentrations of oxygen in the root zone on growth of the vine were rapid with substantial reductions occurring after being exposed to oxygen concentrations in the surrounding water of less than 0.125 mmol l¹ for as little as 1 day. There was no evidence of recovery of growth once aeration was restored to the roots, except for the appearance of new roots at the base of the stems of vines that had been waterlogged for less than 5 days. The quantity of new roots grown was inversely related to the time of waterlogging. Although new roots were also found on the control vines, the quantities involved were very much less than for the vines stressed for up to 4 days. No new roots were found for vines waterlogged for more than 4 days. The substantial loss of dry weight of roots of vines waterlogged for more than 3 days was due in part to a lack of growth and to a physical loss of root tissue. The loss of tissue resulted from the detachment of the cortex from the central stele through the dissolution of an entire layer of cortical cells which, in the control vines, were filled with starch. A microscopic examination of the cells of the root from waterlogged vines showed the cortical cells to be generally distorted with much of the intercellular material missing. The closure of the stomata within 2-3 h of the roots being waterlogged and the rapid desiccation of the leaves that followed the closure, was consistent with earlier findings with kiwifruit vines. Some recovery of stomata activity occurred for vines that had been waterlogged for less than 4 days once the oxygen supply to the root was restored. For vines that had their roots submerged for only 1 day, stomatal activity was fully restored 3 days after the vines were removed from the water. In contrast, there was no recovery of stomatal activity for vines that had been waterlogged for more than 3 days. A feature of stomatal behaviour that was not related to the effects of oxygen stress was the cyclic pattern which developed. Each cycle repeated itself every 4-6 days and consisted of a period of high stomatal conductance followed by a sharp decline to a much lower level. A highly significant negative relationship was found between the level of photosynthetically active radiation and stomatal behaviour. It was concluded that the speed with which the roots die and the associated damage to the leaves under anoxic conditions greatly limits the ability of kiwifruit vines to resume growth once oxygen supply to the root has been restored.

Effects of flooding on Eucalyptus camaldulensis and Eucalyptus globulus seedlings

Flooding for up to 40 days induced morphological changes and reduced growth of 6-week-old Eucalyptus camaldulensis and Eucalyptus globulus seedlings. However, the specific responses to flooding varied markedly between these species and with duration of flooding. Both species produced abundant adventitious roots that originated near the tap root and original lateral roots, but only E. camaldulensis produced adventitious roots on submerged portions of the stem. Flooding induced leaf epinasty and reduced total dry weight increment of seedling of both species but growth of E. globulus was reduced more. In both species dry weight increment of shoots was reduced more than dry weight increment of roots, reflecting compensatory growth of adventitious roots. Adaptation to flooding appeared to be greater in E. camaldulensis than in E. globulus. the importance of formation of adventitious roots in flooding tolerance is emphasized.