Early frost damage on Sitka spruce seedlings and the influence of phosphorus nutrition

Transcription

1 Early frost damage on Sitka spruce seedlings and the influence of phosphorus nutrition D. C. MALCOLM AND B. C. Y. FREEZAILLAH Dept. of Forestry and Natural Resources, University of Edinburgh SUMMARY A frost on 8 September 972 caused widespread damage to young Sitka spruce (Picea sitchensis (Bong.) Carr.) plantations. In an experiment designed to examine the interaction of climate and P nutrition on the growth of young transplants in south Scotland damage was greater on plants growing at low elevation and with high P content. This effect was attributed to their extended growth period compared to those with low P supply. The lack of low temperatures prior to the frost resulted in insufficient hardening of tissues to avoid damage from relatively high temperatures. Damage and recovery were assessed by the reduction in height and dry weight increase compared to undamaged plants. INTRODUCTION DAMAGE to young forest trees by unseasonable temperatures is most often due to late spring frosts occurring after the new season's growth has commenced. Adapted provenances of most species avoid autumnal frosts by the hardening of tissues following cessation of growth under photoperiodic control. In the last few years a number of dramatic early autumn frosts have caused damage to recently planted stands of several tree species and, in particular, Sitka spruce (Picea sitchensis (Bong.) Carr.). Damage is usually indicated by the collapse of tissues, discoloration of needles, or failure of the next season's extension growth (Edgren, 970). The effect of nutritional status on subsequent frost damage has often been discussed in connection with the application of fertilizers to nursery crops late in the season. Adverse effects on hardiness have not been found in autumn or winter (Aldhous, 972) and sometimes enhanced resistance has followed late applications of nitrogen or potassium. O'Carrol (973) has suggested that potassium fertilization may induce earlier flushing, thus predisposing the trees to late frost damage. This effect was not found for newly planted Sitka spruce by Benzian et al. (974) but was consistently so for high nitrogen levels and it did result in increased spring frost damage. This paper reports early frost damage to young Sitka spruce established in a field nutritional experiment in which detailed records of temperature were obtained. It was thus possible to relate damage to both temperature and nutritional status and to follow recovery over the following season. Experimental layout In early 972 a 2-year field experiment was established in Greskine Forest, Dumfriesshire (G.R. NT 05060) to assess the influence of phosphorus Current address: c/o Forestry H.Q., Swettenham Rd., Kuala Lumpur, W. Malaysia. Foreitiy, VoL 48. No. 2, 975

2 HO Forestry nutrition on the response of Sitka spruce to different climatic conditions obtained at increasing elevations. One-year-old seedlings were planted in containers of peat compost differentially fertilized in respect of phosphorus (+P and P treatments). The containers were embedded in the soil at five climatic stations (numbered -5) at the positions shown in Fig.. Plant growth and climatic factors were monitored from May 972 to November 973 (Freezaillah, 974). Dry and wet bulb temperatures were measured by calibrated thermistor probes mounted in a radiation shield at 0-9 m above ground, while soil and 500 IT 400 c o CO -* m J Station 5 Nv Station 4 76 m Station 3 ^38 m Distance (m) ~^^ Station 2 / r^^05m _y StaUon 229 m l ^ - ^ ^ FIG. I. Topographic profile through the experimental stations, aspect NE. Arrow denotes approximate upper level of bracken-browning. container temperatures were recorded at 5,0, and 20 cm depths. All measurements were recorded at hourly intervals by a Grant Miniature Recorder (Type D), accurate to ± C. Frost damage A low pressure system developing between Britain and Norway resulted in a slack northerly air stream over Scotland and Ireland on 7 September 972 (Roy. Met. Soc, 972). Conditions favoured the occurrence of a radiation frost and damage was reported from many areas, including west and central Ireland where the frost was, in places, the earliest recorded for 00 years (Mooney, 973). At Greskine a classic inversion of temperatures occurred during the early hours of 8 September and the courses of temperature at Stations, 2, 3, and 5 are given in Fig. 2. For comparison equivalent data from Eskdalemuir (242 m), some 6 km to the south-east, are included. The air temperature fell to o C, or below, for at least 5 h at Station, h at Station 2, and for 2 h at Station 3. The lowest temperature at Station 5 was C at 0500 h. The strikingly rapid rise of 8 C in h was most marked at Station although similar rises were observed at the other sites and for Eskdalemuir. This rate of change suggests mass air movement rather than a normal diurnal increase.

3 Malcolm and Freezaillah Early Frost Damage 4 Damage to the plants at the two lower stations was noted on September during the weekly height growth assessment. No damage was found at other stations. The damage was recorded and classified as follows: Undamaged no visible symptoms of frost damage. Tip damaged terminal foliage browned. Shoot damaged shoot tissue collapsed resulting in stem dieback. The results are given in Table I from which it is clear that damage was most severe at Station and in the +P treatment at both stations. FIG. 2. Hourly air temperatures ( ) and temperatures of containers at 5 cm depth ( + ) for 8 September 972. Screen temperature at Eskdalemuir, 242 m alt. (O) shown for comparison. The weekly trend in mean height growth, based on eighty-five seedlings per treatment, is shown in Table II. The +P treatment obviously had enhanced the weekly height growth at each station and these trees were still in active growth in week 20 when the frost occurred. The P treatment, on the other hand, had virtually ceased height extension. No measurable height growth was achieved by either treatment at Stations and 2 in week 2. Although the damage was detectable within a few days its full extent could not be assessed for some time. The percentage 'dieback' or loss in total height was therefore calculated on the difference between final height in 972 and the height of live tissue at the start of the 973 growing season. Table III shows that 'dieback' was greatest in the +P treatment at Station. This effect was not apparent at Station 2 where 'tip damage' was predominant. The extent of recovery of the frost damaged seedlings during the 973 growing season is given in Table IV, as the proportional reduction in total

4 42 Forestry TABLE I. Inventory of seedling damage at Station i and Station 2 Station Station 2 +P Week /8/72 Week 9 28/8-3/9/72 Week /9/72 Week 2-7/9/72 Undamaged Tip damaged Shoot damaged 5 33 TABLE II. Mean weekly height increment of Sitka spruce cm Station i Station 2 Station 3 Station 4 Station o-io i O O'73 O' O TABLE III. Relative reduction in height of frosted spruce plants Mean height of seedlings cm End of 972 Beginning of 973 % Dieback Station +P P 5-7 io Station 2 +P P TABLE IV. Height and dry weight of undamaged plants (Station j) and of frosted plants (Stations and 2) November ig73 Station 3 Station 0/ /o reduction Station 2 % reduction Mean total height cm Mean total dry wt 2 g p s Mean height based on 25 plants. 2 Per sample of 5 plants.

5 Malcolm and FreezaMah Early Frost Damage 43 height growth and total dry weight attained by the end of the 973 season, compared with Station 3 data where no damage was recorded. DISCUSSION The occurrence of damage, due to the freezing of tissues in plants, depends on the temperature, the rate of cooling, and the degree of hardening previously attained. Christersson (97) has shown that in Norway spruce [Picea abies Karst.) low temperatures do not cause damage in either hardened or unhardened seedlings unless ice crystals are formed. Using a cooling rate of Week No. TABLE Mean Min., C Absolute Min., C V. Weekly minimum temperatures at Station g-o 7-6-Z 7' o a-s 2-O 4 C/h, tissue had to be supercooled to 4-4 C to 07 C before freezing occurred. It is commonly accepted that intracellular ice formation is lethal, whereas intercellular ice is not necessarily so, depending on the degree of dehydration of cell protoplasm. In this experiment the maximum rate of cooling at Station was only 2-5 C/h and the air temperature (at 0-90 m) only reached 2 C and yet stem tissue collapsed and needles were severely damaged. Mazur (969) considers intracellular freezing unlikely at cooling rates less than 5 C/h although Christersson (97) thought it possible at 4 C/h. It seems probable that stem tissue collapse at Station was due to cell dehydration following intercellular freezing. Unhardened Sitka spruce may require less supercooling before freezing than Norway spruce of Swedish origin. In addition the temperature reached by the air at plant level (c. 25 cm) could well be lower than that measured at 0-9 m. Day and Peace (946) describe a gradient of about 3 C between m and 0-05 m above ground during late frosts in May 936. The differential damage between the three stations might be explained by differences in the duration of temperatures below o C. Lack of damage at Station 3 may also be related to topography as it is on a moderate slope and is above the level to which the valley appeared to fill with freezing air as shown by damage to bracken (Fig. ). Neilson et al. (972) examining the influence of rapid cooling on Sitka spruce shoots showed least recovery in photosynthetic rate during late summer and, if ice formation occurred, death ensued. Cold hardening in many plant species is a phasic process induced by low temperature following growth cessation (Weiser, 970). In this experiment the +P treatment (Table II) was still actively extending at the time of the frost whereas the P treatment had practically ceased and was possibly more lignified but both had the same temperature history. Table V shows that in the period

6 H4 Forestry from the warmest week of the year (8 July 972) minimum temperatures were not likely to result in hardening. Clearly the -(- P treatment was in a less hardened condition and thus was more severely damaged. Cessation of extension growth in Sitka spruce is primarily controlled by photoperiod although it can be influenced by temperature (Malcolm and Golding, 974) and also, it seems from this experiment, by nutrient status. Analysis of plant parts (Freezaillah, 974) showed no significant differences in nitrogen and potassium content while the mean P concentration of shoots from + and P treatments was and 0*36 per cent oven dry weight respectively. Christersson (973) was unable to show any influence of potassium, calcium, or magnesium on hardening of 2-week-old Scots pine seedlings grown in nutrient solutions although Aldhous (972) has claimed reductions in frost damage for nursery grown plants which had received late applications of nitrogen or potassium. There seem to be no reports that phosphorus could be implicated in frost susceptibility in young trees. Having suffered greater damage in terms of loss of height (Table III) the +P treatment at Station made only a moderate recovery in height during 973. This can be explained by the destruction of the upper bud system with the loss of the already developed leaf initials. This loss enhanced the reduction in dry weight increase due to a lack of leaf area for photosynthesis. The situation at Station 2, where little shoot damage occurred, is complicated by the action of other climatic factors which resulted in less growth being made at this station. As Station, on the other hand, had demonstrated a greater growth rate than any higher station before the frost, a comparison of recovery with Station 3 will inevitably give a conservative estimate of the true loss through frost damage. Conclusion Frost occurring so early in autumn and over such an extensive area was unusual. In this instance severe damage occurred at higher temperatures and with a slower cooling rate than might have been expected from other experimental evidence. The prolonged warm weather, and associated dry conditions, prior to the frost, resulted in a lack of hardening. The influence of high phosphorus status on extending the period of active growth of the test plants was clearly the main factor enhancing damage. Sitka spruce is capable of recovering from severe frost damage (MacNab, 974) by developing a new shoot system from adventitious buds. Nevertheless, the loss of production through the delay in the trees growing out of potential frost zones and the resulting poor stem form, is of economic importance. ACKNOWLEDGEMENTS The authors are grateful to the Forestry Commission for providing the experimental site and to the Meteorological Office for the Eskdalemuir temperature data.

7 Malcolm and Freezaillah Early Frost Damage 45 REFERENCES Aldhous, J. R. (972). Nursery practice. Bull. For. Cotmtm., Land., No. 43, pp. 84. Benzian, B., Brown, R. M., and Freeman, S. C. R. (974). Effect of late season top dressings of N (and K) applied to conifer transplants in the nursery on their survival and growth on British forest sites. Forestry, 47, Christersson, L. (97). Frost damage resulting from ice crystal formation in seedlings of spruce and pine. Physiol. Plant. 25, ( J 973)- The effect of inorganic nutrients on water economy and hardiness of conifers. Studia Forest. Suecica, 03, 26. Day, W. R., and Peace, T. R. (946). Spring frosts. Bull. For. Commit., Lond., No. 8, pp. in. Edgren, J. W. (970). Growth of frost damaged Douglas fir seedlings. U.S.F.S. Res. Note Pacif. Nthtoest. For. Range Exp. Sta. PNW-2, pp. 8. Freezaillah, B. C. Y. (974). Climatic influences on the growth and uptake of phosphorus by Sitka spruce. Unpubl. Ph.D. thesis, Univ. of Edinburgh. MacNab, J. D. (974). Unusual frost damage. Scott. For. 28 (i), 4-9. Malcolm, D. C, and Golding, C. F. (974). Environmental effects on shoot growth in conifers. Rep. Forest Res., Lond. 974, 72. Mazur, P. (969). Freezing injury in plants. Ann. Rev. Plant Physiol. 20, Mooney, O. V. (973). An unusual frost in September 972. Irish Forestry, 30, 2-4. Neilson, R. M., Ludlow, M. M., and Jarvis, P. G. (972). Photosynthesis in Sitka spruce (Picea sitchensis (Bong.) Carr.). II. Response to temperature. J. appl. Ecol. 9, O'Carrol, N. (973). Chemical weed control and its effect on the response to K fertilization. Irish Forestry, 29 (), Royal Meteorological Society (972). Weather Log, September 972. Weiser, C. J. (970). Cold resistance and injury in woody plants. Science, 69 (3952),

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